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'ERSITY  OF  ILLINOIS  BULLETIN 

Issued  Weekly 

HVA^M  Av  r i APRIL  1,  1918  No.  31 

(Entered  as  second  class  matter  Deo.  11,  1012,  at  tbe  Post  Office  at  Urbnna,  111.,  under  the  Aot  of  Auk.  24, 1012] 


FUEL  ECONOMY  IN  THE  OPERATION 


OF  HAND  FIRED  POWER  PLANTS 


THE  Engineering  Experiment  Station  was  established  by  act  of 
the  Board  of  Trustees,  December  8,  1903.  It  is  the  purpose 
of  the  Station  to  carry  on  investigations  along  various  lines  of 
engineering  and  to  study  problems  of  importance  to  professional  engi- 
neers and  to  the  manufacturing,  railway,  mining,  constructional,  and 
industrial  interests  of  the  State. 


The  control  of  the  Engineering  Experiment  Station  is  vested  in 
the  heads  of  the  several  departments  of  the  College  of  Engineering. 
These  constitute  the  Station  Staff  and,  with  the  Director,  determine 
the  character  of  the  investigations  to  be  undertaken.  The  work  is 
carried  on  under  the  supervision  of  the  Staff,  sometimes  by  research 
fellows  as  graduate  work,  sometimes  by  members  of  the  instructional 
staff  of  the  College  of  Engineering,  but  more  frequently  by  investigators 
belonging  to  the  Station  corps. 

The  results  of  these  investigations  are  published  in  the  form  of 
bulletins,  which  record  mostly  the  experiments  of  the  Station’s  own 
staff  of  investigators.  There  will  also  be  issued  from  time  to  time,  in 
the  form  of  circulars,  compilations  giving  the  results  of  the  experi- 
ments of  engineers,  industrial  works,  technical  institutions,  and  gov- 
ernmental testing  departments. 

The  volume  and  number  at  the  top  of  the  front  cover  page 
are  merely  arbitrary  numbers  and  refer  to  the  general  publications 
of  the  University  of  Illinois:  either  above  the  title  or  below  the  seal  is 
given  the  number  of  the  Engineering  Experiment  Station  bulletin  or  cir- 
cular which  should  be  used  in  referring  to  these  publications. 

For  copies  of  bulletins,  circulars,  or  other  information  address  the 


Engineering  Experiment  Station, 
Urbana,  Illinois. 


UNIVERSITY  OF  ILLINOIS 
ENGINEERING  EXPERIMENT  STATION 


Circular  No.  7 


April,  1918 


FUEL  ECONOMY  IN  THE  OPERATION 
OF  HAND  FIRED  POWER  PLANTS 


Prepared  under  the  Direction  of 

A Committee  consisting  of  A.  C.  Willard,  Professor  of  Heating 
and  Ventilation  (Chairman),  H.  H.  Stoek,  Professor  of  Mining 
Engineering,  0.  A.  Leutwiler,  Professor  of  Machine 
Design,  C.  S.  Sale,  Assistant  Professor  of  Civil 
Engineering  and  Assistant  to  the  Director  of 
the  Engineering  Experiment  Station,  and 
A.  P.  Kratz,  Research  Associate  in 
Mechanical  Engineering 


ENGINEERING  EXPERIMENT  STATION 

Published  by  the  University  of  Illinois,  Urbana 


Digitized  by  the  Internet  Archive 
in  2017  with  funding  from 

University  of  Illinois  Urbana-Champaign  Alternates 


https://archive.org/details/fueleconomyinope00will_0 


CONTENTS 


PAGE 


6 xi. in 
iHi 


I.  Introduction 7 

1.  Purpose 7 

2.  Authorship 8 

II.  Fuels  Available  for  Power  Plant  Use  in  the 

Middle  West 9 

3.  Kinds  of  Fuel 9 

4.  Properties  of  the  Central  Bituminous  Coals  . . 11 

5.  Preparation,  a Factor  Affecting  the  Value  of  Coal  . . 14 

6.  Storage  of  Coal 18 

7.  Storage  Systems 22 

III.  The  Combustion  of  Fuel  and  the  Losses  Attending 

Improper  Firing 24 

8.  Principles  of  Combustion 24 

9.  Significance  of  Draft 26 

10.  Significance  of  C02  in  the  Flue  Gases 29 

11.  Losses  of  Heat  Value 33 

Excess  Air  and  Air  Leaks 34 

Loss  Due  to  the  Presence  of  Combustible  in  the  Ash  . 38 

Loss  Due  to  the  Presence  of  Carbon  Monoxide  in  the 

Flue  Gases 39 

Loss  Due  to  Soot 39 

Loss  Due  to  Moisture  in  the  Coal  and  Air  ...  40 

Loss  Due  to  Heat  in  the  Escaping  Gases  ....  40 

Loss  Due  to  Radiation ...  40 

12.  Significance  of  Smoke 40 

13.  Methods  of  Hand  Firing  ......  41 

14.  Stoker  Firing 42 

3 


(>1346 


CONTENTS  (Continued) 

PAGE 

IV.  Features  of  Boiler  Installation  in  Relation  to 

Fuel  Economy , . . 44 

15.  Boiler  Settings 44 

Foundation 44 

Side  and  End  Walls 44 

Settings  for  Horizontal  Return  Tubular  Boilers  . 45 

Settings  for  Water  Tube  Boilers 48 

Defects  in  Settings 50 

V.  Installation  Features  Affecting  Draft  Conditions  52 

16.  Stacks  and  Breechings 52 

The  Stack  Damper  and  Its  Use 52 

“Draft”  is  in  Reality  a Pressure 54 

Air  Leaks  Affect  the  Draft  and  Waste  Coal  ...  56 

Breechings  for  a Battery]  of  Two  or  More  Boilers  . 57 

Conditions  Under  Which  a Stack  will  Operate  Eco- 
nomically   57 

VI.  Feed  Water  Heating  and  Purification  as  Factors  in 

Fuel  Economy 60 

17.  Feed  Water  Purification 60 

18.  Treatment  of  Feed  Waters 61 

Chemical  Treatment 61 

Heat  Treatment 61 

Combined  Chemical  and  Heat  Treatment  ....  62 

19.  Boiler  Compounds 62 

20.  Feed  Water  Heaters 62 

Exhaust  Steam  Heaters 63 

Closed  Heaters 63 

Advantages  and  Disadvantages  of  Exhaust  Steam 
Heaters 64 

21.  Economizers 65 

22.  Live  Steam  Heaters 65 

23.  Feeding  Boilers 65 


CONTENTS  (Concluded) 


5 


PAGE 

VII.  Steam  Piping  Requirements  for  Fuel  Economy  in 

Small  Plants 67 

24.  Possibility  of  Fuel  Loss  in  the  Transmission  of  Steam  . 67 

25.  Value  of  High  Pressure  Drips  as  Hot  Feed  Water  . . 67 

26.  Leakage  Losses  at  Valves  and  Fittings 67 

27.  Size  of  Steam  and  Exhaust  Mains 68 

28.  Heat  Insulating  Materials  Required  on  Piping,  Boilers 

and  Breechings 73 

29.  Requirements  for  a Good  Covering 77 

30.  Bad  Effects  of  Water  of  Condensation  in  Steam  Lines  . 78 

31.  Uncovered  Pipes  Waste  Steam  as  Well  as  Coal  . . .78 

VIII.  Record  of  Operation 81 

32.  Purpose  of  the  Record 81 

33.  Character  of  the  Record 81 

34.  Profit  Sharing  or  Bonus  Systems 84 

IX.  Summary  of  Conclusions 85 

35.  Conclusions 85 

Coal 85 

Principles  to  be  Observed  in  Firing 85 

Features  of  Boiler  Installation 86 

Stacks  and  Breechings 87 

Feed  Water  and  Fuel 87 

Steam  Piping  Requirements 88 

Record  of  Operation 88 


LIST  OF  FIGURES 

NO.  . PAGE 

1.  Map  Showing  the  Locations  of  the  Coal  Fields  of  Illinois,  Indiana,  and 

Western  Kentucky 15 

2.  Chart  Showing  the  Theoretical  Value  of  Coals  of  Different  Heating  Values 

at  Various  Prices  per  Ton  . 19 

3.  Manometer  Tube  for  Showing  the  Difference  in  Pressure  between  the  Out- 

side and  the  Inside  of  Boiler  Wall 27 

4.  Sketch  Showing  the  Correct  Method  of  Connecting  Draft  Gages  ...  28 

5.  Apparatus  for  Determination  of  C02  in  Flue  Gas 30 

6.  Sketch  Showing  the  Proper  Location  for  Gas  Sampling  Tubes  to  Avoid 

Damper  Pockets  for  Both  Front  and  Rear  Take-off 32 

7.  Curve  Showing  Relation  between  Excess  Air  and  C02  in  Flue  Gas  . . 37 

8.  Hartford  Setting  for  Return  Tubular  Boilers 45 

9.  Double  Arch  Bridge  Wall  Setting  for  Smokeless  Combustion  ....  46 

10.  Sketch  Showing  Effects  of  Baffling  and  Dampers  in  Causing  Pockets  and 

Eddies  in  the  Flue  Gas  Stream 50 

11.  An  Approved  Form  of  Hinged  Damper 52 

12.  Isometric  Sketch  Illustrating  the  Principle  that  Light  Fluids  or  Gases  are 

Pushed  Upward  when  in  Contact  with  Heavier  Fluids  or  Gases  . . 55 

13.  Sketch  Showing  Variations  in  Draft  at  Different  Points  and  Indicating 

Tendency  Toward  Air  Leakage 56 

14.  Stack  and  Breeching  Connections  for  a Battery  of  Three  Boilers  ...  58 

15.  Diagrammatic  Section  and  Energy  Transformation  Chart  for  Small 

Steam  Power  Plant 70 

16.  Chart  Showing  Amount  of  Heat  Transmitted  by  Steam  Pipes  Insulated 

with  Commercial  Coverings 75 

17.  Chart  Showing  Heat  Lost  by  Bare  Steam  Pipe  and  Saving  which  may 

be  Secured  by  Using  a Good  Covering 76 

18.  Diagram  Showing  Comparative  Saving  in  Water  and  Steam  to  be  Effected 

by  Covering  Live  Steam  Mains 79 

LIST  OF  TABLES 

NO.  PAGE 

1.  Analyses  of  Coals  of  Illinois,  Indiana,  and  Western  Kentucky  ...  12 

2.  Sizes  of  Central  Bituminous  Coals 17 

3.  Stack  Sizes  Based  on  Kent’s  Formula 54 

4.  Impurities  in  Feed  Waters,  Their  Effects  and  Remedies 60 

5.  Coal  and  Steam  Loss  Based  on  100  Feet  of  Uncovered  Steel  Pipe  ...  74 

6 


FUEL  ECONOMY  IN  THE  OPERATION  OF  HAND  FIRED 
POWER  PLANTS 


I.  Introduction 

1.  Purpose.— The  need  for  greater  economy  in  the  use  of  coal 
is  too  apparent,  under  present  conditions,  to  need  emphasis.  The 
demand  for  coal  is  unprecedented,  and  production  is  proceeding  at  a 
rate  which  is  barely,  or  perhaps  not  quite,  keeping  pace  with  the 
demand.  The  U.  S.  Geological  Survey  reports  that,  during  1917,  ap- 
proximately 545,000,000  tons  of  bituminous  coal  were  produced  and 
used  in  the  United  States.  The  demand,  moreover,  is  increasing  at 
the  rate  of  about  ten  per  cent  per  year,  so  that  at  present  the  rate  of 
consumption  is  about  600,000,000  tons  per  year.  Illinois  produces 
about  12 y2  per  cent  of  this  amount,  or  78,000,000  tons.* 

Approximately  45,000,000  tons  of  bituminous  coal  are  used  with- 
in the  state  of  Illinois,  and  of  this  amount  about  6,000,000  tons  are 
consumed  in  hand  fired  power  plants.  It  is  believed  to  be  within  the 
limits  of  practical  attainment  to  effect  a saving  of  from  12  to  15  per 
cent  of  this  fuel.  Expressed  in  tons  and  dollars,  such  a saving  amounts 
to  750,000  tons,  or  $3,500,000.  The  possible  saving  in  the  case  of  many 
individual  plants  is  much  greater  than  the  percentage  stated. 

It  is  the  purpose  of  this  circular  to  present  to  owners,  managers, 
superintendents,  engineers,  and  firemen  of  hand  fired  power  plants 
certain  suggestions  which,  it  is  believed,  will  help  them  in  effecting 
greater  fuel  economy  in  the  operation  of  their  plants,  and  in  deter- 
mining the  properties  and  characteristics  of  the  coal  purchased.  Fea- 
tures of  installation  essential  to  the  proper  combustion  of  fuel  are  dis- 
cussed and  their  importance  emphasized;  the  practice  to  be  observed 
in  the  operation  of  the  plant  is  outlined ; and  the  employment  of  sim- 
ple devices  for  indicating  conditions  of  operation  is  prescribed. 

Special  attention  is  called  to  the  fact  that,  to  secure  the  greatest 
degree  of  success,  cooperation  between  owners  and  managers,  and  the 
men  who  fire  the  coal  is  essential.  Mechanical  devices  to  increase 


* It  is  estimated  that  Illinois  will  produce  more  than  85,000,000  tons  of  coal  in  1918. 


7 


8 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


efficiency  in  the  use  of  coal  cannot  produce  satisfactory  results  un- 
less the  firemen  who  handle  them  are  impressed  with  the  importance 
of  their  duties.  While  the  suggestions  presented  apply  particularly 
to  hand  fired  plants  and  no  attempt  is  made  to  define  practice  for 
stoker  fired  plants,  many  of  the  factors  affecting  fuel  economy  are 
common  to  all  power  plants,  and  for  this  reason  much  of  the  informa- 
tion contained  herein  will,  no  doubt,  be  helpful  to  those  interested  in 
more  economical  operation  of  stoker  fired  power  plants. 

To  the  experienced  engineer  much  that  is  presented  here  will  seem 
elementary  apd  inadequate.  If,  however,  the  plant  owner  who  is 
not  familiar  with  the  extreme  refinements  of  practice  may  obtain  here 
the  facts  which  will  enable  him  to  improve  his  results  to  the  extent  of 
the  modest  saving  suggested,  the  purpose  of  the  publication  will  have 
been  fulfilled. 

2.  Authorship. — The  information  contained  in  this  circular  has 
been  compiled  under  the  direction  of  a committee  consisting  of  A.  C. 
Willard,  Professor  of  Heating  and  Ventilation  (Chairman),  II.  H. 
Stoek,  Professor  of  Mining  Engineering,  0.  A.  Leutwiler,  Profes- 
sor of  Machine  Design,  C.  S.  Sale,  Assistant  Professor  of  Civil  Engi- 
neering and  Assistant  to  the  Director  of  the  Engineering  Experiment 
Station,  and  A.  P.  Kratz,  Research  Associate  in  Mechanical  Engi- 
neering. 

This  committee  has  had  the  assistance  of  an  advisory  committee 
consisting  of  Joseph  Harrington,  Advisory  Engineer  on  Power  Plant 
Design  and  Operation,  Chicago,  Arthur  L.  Rice,  Editor,  Power  Plant 
Engineering , Chicago,  John  C.  White,  Chairman,  Educational  Com- 
mittee, National  Association  of  Stationary  Engineers,  Madison,  Wis., 
O.  P.  Hood,  Chief  Mechanical  Engineer,  Bureau  of  Mines,  Washing- 
ton, D.  C.,  D.  M.  Myers,  Advisory  Engineer  on  Fuel  Conservation, 
United  States  Fuel  Administration,  Washington,  D.  C.,  and  C.  R. 
Richards,  Dean  of  the  College  of  Engineering  and  Director  of  the 
Engineering  Experiment  Station  of  the  University  of  Illinois.  Each 
member  of  this  Advisory  Committee  personally  reviewed  the  original 
manuscript  and  a meeting  was  held  at  Urbana  on  March  21,  1918,  at 
which  the  work  was  examined  in  detail.  The  authors  gratefully  ac- 
knowledge the  valuable  assistance  and  cooperation  of  the  members 
of  this  committee  and  feel  that  the  value  of  the  publication  has  been 
greatly  enhanced  as  a result  of  their  efforts. 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


9 


II.  Fuels  Available  for  Power  Plant  Use  in  the  Middle  West 

3.  Kinds  of  Fuel. — The  varieties  of  fuel  used  by  hand  fired 
power  plants  in  Illinois  are : 

Central  bituminous  coals  as  represented  by  those  from  the  coal 
fields  of  Illinois,  western  Kentucky,  and  Indiana. 

Eastern  bituminous  and  semi-bituminous,  or  soft  coals,  from  the 
Pennsylvania,  West  Virginia,  and  eastern  Kentucky  fields. 

A classification  of  solid  fuels  available  for  this  purpose  will,  of 
course,  include  anthracite  and  coke  but  none  of  these  is  used  to  any 
considerable  extent  for  power  purposes  in  Illinois.  The  liquid  fuel, 
petroleum,  is  produced  in  large  quantities  in  Illinois  but  is  not  used 
directly  for  fuel  purposes  to  any  great  extent. 

All  these  coals  are  composed  of  the  following  materials  in  varying 
proportions  : 

(1)  Solid  or  fixed  carbon  which  burns  with  a glow  and  without 
flame. 

(2)  Gases  or  volatile  materials  which  escape  from  the  coal  when 
it  is  heated  and  which  burn  with  a flame. 

(3)  Gases  or  volatile  matter  and  water  which  escape  from  the 
coal  when  it  is  heated  and  which  do  not  burn. 

(4)  Ash  or  mineral  matter  which  does  not  burn  and  which 
remains  as  ashes  after  the  coal  is  burned. 

The  relative  proportions  of  these  materials  in  different  coals 
determine  their  value  for  particular  purposes.*  Fuels  having  a large 
amount  of  fixed  carbon  and  a relatively  small  amount  of  volatile 
matter  burn  with  a short  flame  and  the  whole  process  of  combustion 
takes  place  at  or  near  the  surface  of  the  fuel  bed.  Such  fuels  can 
be  burned  without  developing  visible  smoke.  On  the  other  hand  coals 
containing  a relatively  large  amount  of  volatile  matter  and  a lower 
proportion  of  fixed  carbon  burn  with  a longer  flame  and  tend  to  pro- 
duce more  visible  smoke  than  the  high  carbon  coals  because  the  volume 
of  combustible  gases  distilled  from  them  is  greater. 

The  bituminous  coals  of  the  central  field  (Illinois  type)  contain 


* The  “fuel  ratio,”  which  is  the  quotient  obtained  by  dividing  the  fixed  carbon  by  the 
volatile  matter,  is  often  used  as  a means  of  classifying  coals,  and  for  bituminous  coals  it 
answers  fairly  well. 


10 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


from  40  to  55  per  cent  of  fixed  carbon,  10  to  25  per  cent  of  com- 
bustible gas,  5 to  15  per  cent  of  non-combustible  gas,  8 to  15  per  cent 
of  moisture,  and  8 to  15  per  cent  of  ash.  When  improperly  fired  or 
burned  in  furnaces  not  adapted  to  their  use,  central  bituminous  coals 
give  off  so  large  an  amount  of  sooty  material  that  flues  are  often 
quickly  clogged.  These  unconsumed  volatile  products  also  represent 
a direct  loss  of  heat  value.  Coals  of  the  Illinois  type  ignite  easily 
and  burn  freely. 

Because  the  amount  of  solid  carbon  in  most  Illinois  coal  is  lower 
and  the  percentage  of  ash  and  moisture  higher  its  heating  value  is 
usually  less  than  that  of  most  eastern  bituminous  coals,  but  the  cost 
is  usually  so  much  less  that  it  is  more  economical  to  use  local  coals. 
At  this  time  (March,  1918)  the  transportation  of  fuel  over  long  dis- 
tances is  not  only  undesirable,  but  it  is  practically  impossible,  and 
bituminous  coals  of  the  central  field  constitute  the  only  fuel  available 
in  quantities  for  use  in  Illinois. 

The  moisture  and  non-combustible  gases  present  in  all  coals  are 
detected  only  by  chemical  analysis.  They  not  only  do  not  produce 
heat,  but  represent  a definite  loss  because  they  absorb  and  carry  off 
heat  which  would  otherwise  be  available  for  useful  purposes.  The 
term  moisture  in  coal  does  not  mean  the  water  adhering  to  the  sur- 
face of  the  lumps,  but  that  contained^  within  the  pores  of  the  coal.  A 
coal  containing  a high  percentage  of  moisture  by  analysis  may  appear 
perfectly  dry. 

The  ash  content  of  different  coals  varies  greatly.  Ash  is  non- 
combustible mineral  matter  which  not  only  has  no  heating  value  and, 
therefore,  represents  a portion  of  the  coal  from  which  no  return  is 
received,  but  it  may  hinder  the  free  burning  of  the  combustible  com- 
ponents of  the  coal.  If  the  ash  contains  certain  mineral  substances, 
it  may  by  clinkering  greatly  interfere  with  the  process  of  firing  and 
with  the  cleaning  of  grates.  The  ash  normally  is  removed  through 
the  ashpit  into  which  often  passes  also  a certain  amount  of  unburned 
coal.  For  this  reason  the  amount  of  ashes  removed  from  the  pit  usu- 
ally represents  a larger  percentage  of  the  fuel  fired  than  the  analysis 
of  the  ash  content  indicates.  It  should  be  clearly  understood  that 
ash  will  not  burn  and  that  no  treatment  with  chemicals,  or  “secret 
processes,  ” will  cause  it  to  burn.  Likewise,  it  is  not  possible  to  increase 
the  heat  value  of  coal  by  treating  it  chemically  or  by  adding  a nostrum 
to  it. 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


11 


The  ash  in  coal  may  be  divided  into  two  classes ; first,  that  which 
is  a definite  part  of  the  composition  of  the  coal  and  which  cannot  be 
separated  from  the  coal  by  hand  or  by  mechanical  process,  and,  sec- 
ondly, that  which  is  due  to  rock,  slate,  and  shale  which  become  mixed 
with  the  coal  in  mining  and  which  can  in  a large  measure  be  separated 
from  the  coal  either  in  the  mine  or  in  the  tipple. 

Bituminous  coal  may  be  either  of  the  coking  or  the  non-coking 
variety.  Coals  vary  widely  with  reference  to  their  coking  properties. 
A true  coking  coal  when  fired  swells,  becomes  pasty  and  fuses  into  a 
mass  of  more  or  less  porous  coke.  Such  coke  will  burn  without  flame 
and  will  hold  fire  for  a considerable  period.  This  fusing  or  coking 
takes  place  without  respect  to  the  size  of  the  piece  of  coal.  A non- 
coking coal  does  not  swell  and  become  pasty  but  burns  away  gradu- 
ally to  ash,  the  pieces  becoming  gradually  smaller  and  smaller.  There 
is  a gradual  gradation  from  true  coking  to  true  non-coking  coals  and 
many  coals  cannot  be  distinctly  placed  in  either  class.  Coal  which 
will  not  coke  on  a furnace  grate  may,  however,  give  good  coke  in  by- 
product coke  ovens,  particularly  when  mixed  with  other  more  easily 
coking  coals.  This  is  the  case  with  many  Illinois  coals. 

The  eastern  bituminous  coals  contain  from  5 to  10  per  cent  of 
ash,  from  25  to  35  per  cent  of  combustible  gases,  from  2 to  5 per  cent 
of  moisture  and  non-combustible  gases,  and  from  55  to  65  per  cent  of 
solid  carbon.  They  are  more  generally  of  the  coking  variety  than  are 
the  Middle  West  coals.  In  general,  they  are  higher  in  heating  value 
and  lower  in  ash.  They  are  more  friable  and  are  not  so  well  suited 
for  transportation  and  repeated  handling  as  are  many  of  the  central 
bituminous  coals. 

4.  Properties  of  the  Central  Bituminous  Coals. — Coals  used  in 
Illinois  power  plants  come  mainly  from  the  Illinois,  Indiana  and 
western  Kentucky  fields.  The  properties  of  these  coals  as  disclosed 
by  analyses  of  samples  from  different  localities  are  given  in  Table  1. 

The  average  analyses  of  the  important  Illinois  coals  have  been 
determined  with  great  care.  The  averages  for  Kentucky  were  obtained 
by  average  analyses  of  composite  samples  from  several  mines.  Aver- 
age analyses  are  not  available  for  Indiana  coals  and  instead  analyses 
are  given  of  samples  from  three  important  Indiana  coal  counties, 
namely,  Clay,  Green  and  Sullivan  counties. 


12 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


Table  1 

Analyses  of  Coals  of  Illinois,  Indiana,  and  Western  Kentucky 

(Figures  are  for  face  samples  and  for  coal  “as  received”)! 


District 

Coal 

Bed 

Moisture 

Volatile 

Matter 

Fixed 

Carbon 

Ash 

B.  t.  u. 
(Heating 
Value) 

Illinois  (Average  Analyses) 


La  Salle 

2 

16.18 

38.83 

37.89 

7.08 

10,981 

Murphysboro 

2 

9.28 

33.98 

51.02 

5.72 

12,488 

Rock  Island  and  Mercer  Counties  . . 

1 

13.46 

38.16 

39.75 

8.63 

11,036 

Springfield-Peoria . : 

5 

15.10 

36.79 

37.59 

10.53 

10,514 

Saline  County 

5 

6.75 

35.49 

48.72 

9.04 

12,276 

Franklin  and  Williamson  Counties  . . 

6 

9.21 

34.00 

48.08 

8.71 

11,825 

Southwestern  Illinois 

6 

12.56 

38.05 

39.06 

10.33 

10,847 

Danville:  Grape  Creek  coal 

6 

14.45 

35.88 

40.33 

9.34 

10,919 

Danville : Danville  coal 

7 

12.99 

38.29 

38.75 

9.98 

11,143 

Indiana  (Typical  Analyses) 


Clay  County 

( Brazil  1 

15. 

.38 

32 

.66 

46. 

.08 

5.88  ‘ 

11,680 

| block  ) 

Greene  County 

IV 

13. 

53 

33 

.54 

45 

.38 

7.55 

11,738 

Greene  County : 

V 

10. 

30 

36 

.31 

41, 

.64 

11.75 

11,218 

Sullivan  County 

IV 

12. 

15 

33 

.48 

46. 

23 

8.14 

11,722 

Sullivan  County 

V 

12. 

,14 

35 

.17 

43. 

73 

8.96 

11,516 

Sullivan  County 

VI 

14. 

86 

31 

.65 

46. 

14 

7.35 

11,324 

Kentucky  (Average  of  Composite  Samples) 


9 

8.17 

36.82 

45.17 

9.83 

11,867 

11 

7.33 

38.28 

45.28 

9.11 

12,056 

12 

9.67 

34.86 

46.46 

9.01 

11,695 

1“  As  received”  samples  represent  the  coal  as  taken  from  the  mine.  It  is  probable  that  the  values 
given  are  fairly  representative  of  the  coals  as  purchased  from  local  dealers. 


A study  of  the  values  presented  in  Table  1 reveals  the  following 
facts : 

(1)  The  amount  of  ash  in  the  various  coals  as  they  exist  in  the 
mine  varies  within  a range  of  about  6 per  cent.  With  in- 
adequate preparation  of  the  coal  for  the  market,  however,  the 
range  of  difference  may  be  as  much  as  12  or  15  per  cent. 

(2)  There  is  a variation  in  the  percentage  values  over  a range 
of  about  5 per  cent  in  the  volatile  matter  in  the  different  coals, 
an  amount  which  is  negligible  in  view  of  the  proportionately 
greater  variations  in  heating  value  and  in  ash. 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


13 


(3)  The  variation  in  the  amount  of  moisture  present  in  the  dif- 
ferent coals  is  considerable,  but  this  variation  is  reflected  to 
some  extent  in  the  B.  t.  u.*  values.  If  two  coals  have  about 
the  same  amount  of  fixed  carbon,  volatile  matter  and  ash,  the 
coal  having  the  higher  moisture  content  has  the  lower  B.  t.  u. 
value.  Accordingly,  if  the  B.  t.  u.  value  of  a coal  is  known, 
the  moisture  content  is  not  important.  This  statement  is  also 
true  as  regards  ash,  except  that  the  ash  represents  a residue 
to  be  handled. 

With  regard  to  the  B.  t.  u.  values,  the  table  shows  that  there  are 
important  and  distinguishable  differences  in  the  heating  quality  of 
the  different  coals  found  in  the  three  states,  yet  the  extent  of  dif- 
ference is  not  sufficient  to  justify  extravagant  statements  in  praise  of 
certain  coals  or  in  disparagement  of  others.  On  the  basis  of  heating 
value  alone,  the  difference  between  the  value  of  the  poorest  and  that 
of  the  best  coals,  as  they  are  found  in  the  mine,  amounts  to  about  one- 
fifth  of  the  value  of  the  poorest  coal.f  As  stated  previously,  however, 
the  care  with  which  coal  is  prepared  affects  its  value  as  fuel  (see  sec- 
tion 5 ‘‘Preparation,  a Factor  Affecting  the  Value  of  Coal,”  p.  14). 

The  values  given  cover  the  most  wide-spread  and  most  important 
coal  beds  of  Illinois,  Indiana,  and  western  Kentucky.  It  should  be 
observed  that  the  variations  are  as  great  between  coals  which  come 
from  the  same  bed  in  widely  separated  localities  as  between  coals 
which  come  from  different  beds,  for  instance,  the  No.  6 coal  of  Frank- 
lin and  Williamson  counties  differs  nearly  as  much  from  the  No.  6 
coal  of  the  Belleville  region  of  southwestern  Illinois  as  it  does  from 
the  No.  5 coal  of  Saline  County.  For  large  areas,  however,  the  char- 
acteristics of  each  bed  are  remarkably  constant  and  variations  in  the 
character  of  the  coal  are  regional  rather  than  local.  It  is  possible 
therefore,  to  subdivide  the  large  coal  fields  of  the  three  States  into 
districts  as  shown  on  the  accompanying  map  (Fig.  1). 

The  subdivisions  of  the  Illinois  field  as  shown  on  this  map  were 
based  mainly  upon  geological  conditions  and  upon  the  general  sim- 

* For  a definition  of  B.  t.  u.  see  foot-note  on  page  17. 

t Comprehensive  tables  giving  analytical  values  for  Illinois  coals  are  contained  in  Bui. 
29  of  the  State  Geological  Survey,  Urbana,  111.,  entitled  “Purchase  and  Sale  of  Illinois  Coal 
under  Specifications,”  by  S.  W.  Parr,  and  in  Bui.  3 of  the  Illinois  Coal  Mining  Investiga- 
tions, Urbana,  HI.,  entitled  “Chemical  Study  of  Illinois  Coals,”  by  S.  W.  Parr.  Professional 
Paper  100A,  U.  S.  Geological  Survey,  Washington,  D.  C.,  contains  analyses  of  coals  from 
all  parts  of  the  United  States. 


14 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


ilarity  in  the  methods  of  mining  in  each  district  rather  than  upon  a 
difference  in  the  quality  of  the  coal.  This  fact  should  be  understood 
in  considering  the  analyses  of  coals  from  the  different  districts.  For 
instance,  the  coals  from  the  eastern  part  of  Perry  County  are  very 
similar  to  those  from  Franklin  and  Williamson  counties,  although 
classed  by  the  map  as  being  in  a different  district.  The  dividing  line 
accepted  by  the  Illinois  Coal  Mining  Investigations  between  District 
6 and  the  southern  part  of  District  7 is  the  Duquoin  anticline,  a dis- 
tinct geologic  structural  feature  which  has,  however,  not  effected  any 
distinct  change  in  the  character  of  the  coal,  that  just  west  of  and  near 
the  anticline  being  practically  of  the  same  quality  as  that  east  of  the 
anticline  in  the  same  locality. 

The  several  Illinois  coals  do  not  differ  materially  in  appearance 
and  it  is  often  difficult  to  distinguish  one  from  another  without  more 
careful  tests  than  the  ordinary  purchaser  can  make.  The  apparent 
difference  is  frequently  due  to  preparation  rather  than  to  actual  differ- 
rences  in  chemical  composition  and  in  heating  quality. 

5.  Preparation,  a Factor  Affecting  the  Value  of  Coal. — Coal  oc- 
curs in  the  earth  in  beds  or  seams,  and  usually  in  a solid  mass  as  a rock. 
In  mining  it  is  blasted  with  powder,  shoveled  into  cars,  and  conveyed 
to  the  surface.  In  the  process  of  mining  and  handling  it  becomes 
broken  up  into  pieces  of  all  sizes.  It  may  have  some  rock  or  dirt  from 
the  floor  and  roof  of  the  mine  mixed  with  it  or  there  may  be  bands 
or  layers  of  earthy  matter  in  the  coal  seam  itself.  Coal  as  it  comes 
from  the  mine  is  therefore  not  usually  in  condition  for  immediate 
delivery  to  the  consumer,  but  ordinarily  must  first  be  “ prepared’ 1 in 
order  to  remove  these  impurities  and  to  separate  it  into  the  proper 
sizes  for  various  purposes  or  markets.  The  impurities  in  the  large  sizes 
of  coal  are  removed  by  picking  them  out  by  hand,  and  in  the  smaller 
sizes  by  treating  the  coal  in  cleaning  machinery.  Separation  into  dif- 
ferent sizes  is  accomplished  by  sending  the  coal  over  screens  having 
holes  of  the  proper  size. 

Table  2 gives  the  customary  sizes  and  the  corresponding  names  of 
central  bituminous  coals  as  they  are  available  in  the  market. 


9Cf 


99* 


88* 


bukkn 


tlvjnoliT 


N Kf' 
W'jmMicfe 


vltknxedUo 


STTL 


jwqw 


|y 


r\S^KF^Kvii 

^iin^nn  . J/ 


•jAU) 


Coal  Fields  op  Illinois, Indiana,  A ^ 1 ; f 'V*  JK«  ^ v^ifs  ‘K  -‘t1:' 

and  Western  Kentucky  *-t» '4—^4*— * — ■ — Sfe  i ~S«,4li»'tyL  i ( 

Districts  for  Classification  of  \8L'>iV>X  t 7 ^ r-1f’VN  ' 1,111 

Coals  in  Illinois  \ I*£jU„  | } ftakf  " \ij_  ) ^ ^ 

jl.  Longwall  district:  No.  2 coal  . 1 VpTwr 

! (“Third  Vein”)  JM/f&tfLr  wM‘<  N 

12.  Jackson  County  district:  No.  2 T'I;  kT-'^x  Vf  n.  — VVaiJiW-^T’-1'' 

i coal  (“Murphysboro”  coal:  M&j,'  ,.  \S  V,SrWfj  i,  yo  .-V1”  “ T "V 

■ 3-  *$£,  n “f .“i Mercer  oooa-  :% Sa ' < > - V 

4.  Peoria-Springfield  district:  No.  5 coal  (“Central  Illinois”  coal) ?V''  VdiFtfsnAX|  | \ 

5.  Saline  and  Gallatin  counties:  No.  5 coal  (“Harrisburg”  coal)  ’ / &'¥VA  jTOU|,lr'i  *\£. 

6.  Franklin,  Williamson,  and  Jefferson  counties:  No.  6 coal  (“Franklin- Williamson”  coal)  % 

7.  Southwestern  Illinois:  No.  6 coal 

8.  Danville  district:  No.  6 and  No.  7 coal  (“Grape  Creek”  and  “Danville”  coals)  v 

(Note:  The  districts  as  indicated  in  this  list  were  arranged  for  convenience  of  classification  IT,:- .< 

of  the  coals  by  the  Illinois  Coal  Mining  Investigations;  they  do  not  correspond  to  theSfeta 
j Mine  Inspectors’  districts  nor  to  the  trade  subdivisions.) 


tf^OKU 

■vet§m^A^' 


_i7j  ' 

V 

1 

Fig.  1.  Map  Showing  the  Locations  of  the  Coal  Fields  of  Illinois, 
Indiana,  and  Western  Kentucky 


THE  LIBRARY 
OF  THE 

UKivsasiiv  e»:  ill::::'; 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


17 


Table  2 

Sizes  of  Central  Bituminous  Coals 


Name 

Size  op  Pieces 

Run  of  Mine 

Mixture  of  all  sizes 

Lump 

Large  lumps  separated  from  the  finer  sizes 

Egg  or  Furnace 

Lumps  3-6  inches 

No.  1 Nut  or  Small  Egg 

2-3  inches 

No.  2 Nut  or  Stove 

1M_2  inches 

No.  3 Nut  or  Chestnut 

inches 

No.  4 Nut  or  Pea  or  Buckwheat 

inch 

No.  5 Nut 

Under  M inch 

Screenings 

A mixture  of  all  sizes  under  2 inches 

For  large  power  plants  the  custom  of  purchasing  coal  on  the 
B.  t.  u.*  basis  is  increasing  and  if  the  specifications  for  such  purchase 
are  properly  drawn  and  understood  it  is  the  logical  way  to  buy  coal,  be- 
cause it  is  equivalent  to  buying  so  many  heat  units  instead  of  so  many 
tons  of  coal.  Upon  this  basis  a purchaser  should  be  able  to  determine 
whether  a low  priced  coal  which  gives  less  efficient  boiler  service  and 
involves  greater  expense  for  handling  ashes  is  really  cheaper  than  a 
higher  priced  coal. 

With  reference  to  the  selection  of  different  Illinois  coals,  the 
B.  t.  u.  value  and  the  percentage  of  ash  furnish  a general  guide  to  their 
relative  values.  If  two  coals  are  otherwise  alike  in  composition,  the 
ash  content  increases  as  the  B.  t.  u.  value  decreases;  hence  their  rel- 
ative values  may  be  expressed  with  fair  accuracy  by  either  the  B.  t.  u. 
or  the  ash  value  alone,  although  the  evaporative  value  of  any  coal 
drops  off  more  rapidly  than  its  B.  t.  u.  value  when  the  ash  content 
exceeds  10  or  15  per  cent.  A close  approximation  of  the  percentage  of 
actual  heat  producing  material  in  Illinois  coal  may  be  obtained  by 
dividing  the  B.  t.  u.  value  of  the  coal  by  155.  Thus,  a 12,000  B.  t.  u. 
coal  contains  12,000  -f- 155,  or  77  per  cent  of  heat-producing  mate- 
rial. In  order  to  enable  the  small  consumer  to  judge  the  relative  values 
of  coals  offered  at  different  prices,  the  chart,  Fig.  2,  has  been  prepared 

* B.  t.  u.  is  a term  made  use  of  by  engineers  to  express  a certain  amount  of  heat.  It 
is  an  abbreviation  of  “British  thermal  unit.”  One  B.  t.  u.  is  the  amount  of  heat  required 
to  raise  the  temperature  of  one  pound  of  water  one  degree  Fahrenheit.  If  a coal  has  a 
heating  value  of  14,000  B.  t.  u.,  there  is  sufficient  heat  in  one  pound  of  it  to  raise  14,000 
pounds  of  water  one  degree  Fahrenheit. 


18 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


to  show  the  theoretical  value  of  coals  of  different  heating  or  B.  t.  u. 
values  at  various  prices  per  ton. 

It  should  be  understood  that  the  purchase  of  coal  on  the  B.  t.  u. 
basis  does  not  insure  a maximum  evaporative  value  from  the  fuel,  be- 
cause a high-grade  coal  carelessly  fired  may  give  poorer  results  than 
a low-grade  coal  carefully  fired.  In  other  words,  the  B.  t.  u.  value 
of  a coal  is  simply  an  indication  of  what  should  be  obtained  with  care- 
ful firing  and  the  person  who  furnishes  coal  of  a high  B.  t.  u.  value 
cannot  be  held  responsible  for  poor  results  obtained  from  that  coal 
through  improper  use.  It  should  also  be  remembered  that  while  the 
B.  t.  u.  value  shows  the  chemical  composition,  it  indicates  nothing  with 
regard  to  the  physical  properties  of  the  coal,  and  these  properties  may 
be  equally  as  important  as  the  chemical  properties  in  their  effects  upon 
firing,  storing,  and  transportation. 

6.  Storage  of  Coal. — The  storage  of  a certain  amount  of  coal  by 
every  power  plant  is  both  desirable  and  essential  in  order  to  insure 
continuous  operation.  Although  there  is  some  misapprehension  with 
regard  to  the  practicability  of  storing  bituminous  coal,  a study  of  the 
subject  based  upon  the  reported  experience  of  more  than  a hundred 
firms  and  individuals  indicates  that  the  difficulties  attending  storage 
are  not  serious.*  These  investigations  have  shown  that: 

(1)  It  is  practicable  and  advantageous  to  store  coal,  not  only 

during  war  times,  but  also  under  normal  conditions,  near 
the  point  of  consumption.  The  practice  of  storing  coal  has 
the  advantage  of  (a)  insuring  the  consumer  a supply  of  coal 
at  all  times,  (b)  permitting  the  railroads  to  utilize  their  cars 
and  equipment  to  the  best  advantage,  and  (c)  permitting 
the  mines  to  operate  at  a more  nearly  uniform  rate  of  produc- 
tion throughout  the  year.  The  expense  of  storage  may  be 
regarded  as  the  expense  of  insurance  against  shut-downs. 

(2)  Certain  requirements  affecting  the  kinds  and  sizes  of  coal 

must  be  observed  as  follows : 

(a)  Most  varieties  of  bituminous  coal  can  be  stored  successfully 
if  of  proper  size  and  if  free  of  fine  coal  and  dust.  The  coal 
must  be  so  handled  that  dust  and  fine  coal  are  not  produced 

* For  a more  nearly  complete  discussion  of  the  problem  of  coal  storage,  see  Bulletin  97 
of  the  Engineering  Experiment  Station,  University  of  Illinois,  entitled  “Effects  of  Storago 
Upon  the  Properties  of  Coal,”  by  S.  W.  Parr,  and  Circular  6 of  the  Engineering  Experiment 
Station,  University  of  Illinois,  entitled  “The  Storage  of  Bituminous  Coal,”  by  H.  H.  Stock. 


Fig.  2.  Chart  Showing  the  Theoretical  Value  of  Coals  of  Different  Heating  Values  at  Various  Prices  Per  Ton 

To  make  a comparison  between  coals  of  different  B.  t.  u.  values,  locate  the  point  on  the  line  representing  the  B.  t.  u.  value  of  the  coal  in  question 
directly  opposite  the  price  involved.  Through  this  point  draw  a vertical  line,  and  from  the  intersection  of  this  with  the  diagonal  lines  representing 
any  other  B.  t.  u.  value  read  the  comparable  price  from  the  price  scale  at  the  left.  For  Example:  If  a 12,000  B.  t.  u.  coal  is  offered  at  $7.10  per 
ton,  a coal  having  a heating  value  of  11,000  B.  t.  u.  will  be  worth  $6.45. 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


Price  per  ton  of  coa/. 


I I I I I I I II  I I I I %•> 


Cl  c ?/  //  0l6Q<L°)SPC2l 


20 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


in  excessive  amounts,  and  allowed  to  remain  during  storage. 
Although  some  coals  can  be  stored  with  greater  safety  than 
others,  the  danger  from  spontaneous  combustion  is  due  more 
to  improper  piling  of  the  coal  than  to  the  kind  of  coal  stored. 
The  danger  of  spontaneous  combustion  can  be  very  greatly 
reduced  if  not  entirely  eliminated  by  storing  only  lump  coal 
from  which  the  dust  and  fine  coal  have  been  removed. 

(b)  Fine  coal  or  slack  has  sometimes  been  stored  successfully  in 
cases  in  which  air  has  been  excluded  from  the  interior  of  the 
pile.  Exclusion  of  air  from  the  interior  of  a pile  may  be 
acomplished  (a)  by  a closely  sealed  wall  built  around  the 
pile,  or  (b)  by  very  close  packing  of  the  fine  coal.  A pile  of 
slack  must  be  carefully  watched  to  detect  evidences  of  heat- 
ing and  means  should  be  provided  for  moving  the  coal 
promptly  if  heat  develops.  The  only  absolutely  safe  way 
to  store  slack  or  fine  coal  is  under  water. 

(c)  Many  varieties  of  mine  run  bituminous  coal  cannot  be  stored 
safely  because  of  the  presence  of  fine  coal  and  dust. 

(d)  Coal  exposed  to  the  air  for  some  time  may  become  “sea- 
soned” and  thus  may  be  less  liable  to  spontaneous  combus- 
tion because  of  the  oxidation  of  the  surfaces  of  the  lumps. 
Experience  covering  this  point,  however,  is  by  no  means  con- 
clusive. 

(e)  It  is  believed  by  many  that  damp  coal  or  coal  stored  on  a 
damp  base  is  peculiarly  liable  to  spontaneous  combustion,  but 
the  evidence  on  this  point  also  is  not  conclusive.  It  is  safest 
not  to  dampen  coal  when  or  after  it  is  placed  in  storage. 

(3)  The  sulphur  contained  in  coal  in  the  form  of  pyrites  is  not  the 

chief  source  of  spontaneous  combustion,  as  was  formerly 
supposed,  but  the  oxidation  of  the  sulphur  in  the  coal  may 
assist  in  breaking  up  the  lumps  and  thus  may  increase  the 
amount  of  fine  coal,  which  is  particularly  liable  to  rapid 
oxidation.  The  opinion  is  wide-spread  that,  if  possible,  it  is 
well  for  storage  purposes  to  choose  a coal  with  a low  sulphur 
content. 

(4)  In  piling  coal  for  storage  the  following  conditions  should  be 

observed : 

(a)  To  prevent  spontaneous  combustion,  coal  should  be  so  piled 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


21 


that  air  may  circulate  through  it  freely  and  thus  may  carry 
off  the  heat  due  to  oxidation  of  the  carbon,  or  it  should  be 
so  closely  packed  that  air  cannot  enter  the  pile  and  stimulate 
the  oxidation  of  the  fine  coal. 

(b)  Stratification,  or  segregation  of  fine  and  lump  coal,  should 
be  avoided,  since  an  open  stratum  of  coarse  lumps  of  coal 
may  provide  a passage  or  flue  for  air  to  enter  and  come  in 
contact  with  the  fine  coal,  and  thus  to  oxidize  it  and  start 
combustion. 

(c)  Coal  can  be  stored  with  greater  safety  in  piles  not  more  than 
six  feet  high  than  in  piles  of  greater  height  since  the  coal 
is  more  fully  exposed  to  the  air  in  low  piles,  the  superficial 
area  of  the  pile  in  relation  to  its  volume  being  greater.  The 
coal  pile  should  preferably  be  divided  by  alleyways  so  as  to 
facilitate  the  rapid  removal  of  the  coal  in  case  of  necessity 
and  so  that  an  entire  pile  may  not  be  endangered  by  a local 
fire. 

(d)  The  practice  of  ventilating  coal  piles  by  means  of  pipes  in- 
serted at  intervals  has  not  proved  generally  effective  as  a 
means  of  preventing  spontaneous  combustion  in  storage  piles 
in  the  United  States  and  it  is  not  advised.  Such  practice  is, 
however,  reported  to  have  been  successful  in  certain  parts 
of  Canada. 

(e)  Coals  of  different  varieties  should  not  be  mixed  in  stor- 
age, because  a single  variety  of  coal  which  has  a tendency 
toward  spontaneous  combustion  may  jeopardize  the  safety 
of  the  entire  pile. 

(f)  Storage  appliances  and  arrangements  should  be  designed 
so  as  to  make  it  possible  to  load  out  the  coal  quickly  if  neces- 
sary. Coal  should  positively  not  be  stored  in  large  piles  un- 
less provision  is  made  for  loading  it  out  quickly. 

(g)  Pieces  of  wood,  greasy  waste,  or  other  easily  combustible 
material  mixed  in  a coal  pile  may  form  the  starting  point  of 
a fire,  and  every  precaution  should  be  taken  to  keep  such 
material  from  the  coal  as  it  is  being  placed  in  storage. 

(h)  It  is  very  important  that  coal  in  storage  should  not  be 
affected  by  external  sources  of  heat  such  as  steam  pipes.  The 
susceptibility  of  coal  to  spontaneous  combustion  increases 
rapidly  as  the  temperature  rises. 


22 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


(5)  The  effects  of  storage  on  the  value  and  properties  of  coal  may  be 

summarized  as  follows : 

(a)  The  heating  value  of  coal  as  expressed  in  B.  t.  u.  is  decreased 
very  little  by  storage,  but  the  opinion  prevails  that  storage 
coal  burns  less  freely  than  fresh  coal.  Experiments  indicate 
that  much  of  this  apparent  deficiency  may  be  overcome  by 
keeping  a thin  bed  on  the  grate  and  by  carefully  regulating 
the  draft  to  suit  the  fuel. 

(b)  The  deterioration  of  coal  when  stored  under  water  is  neg- 
ligible, and  such  coal  absorbs  very  little  extra  moisture.  If 
only  part  of  a coal  pile  is  submerged,  the  part  exposed  to  the 
air  is  still  liable  to  spontaneous  combustion. 

(6)  In  order  to  guard  against  loss  in  the  event  of  fire  in  a pile  of 

stored  coal  the  following  facts  should  be  understood: 

(a)  The  best  means  of  preventing  loss  in  stored  coal  is  to  inspect 
the  pile  regularly  and  if  the  temperature  in  any  part  of  the 
pile  rises  to  150  degrees  F.  to  prepare  to  remove  the  coal  from 
the  spot  affected.  If  the  temperature  continues  to  rise  and 
reaches  175  degrees  F.,  the  coal  should  be  removed  as 
promptly  as  possible.  Temperature  readings  may  be  taken 
by  lowering  a thermometer  into  the  interior  of  a pile  through 
a pipe  driven  into  it.  The  common  methods  of  testing  for 
fires  in  coal  piles  are : 

(1)  By  watching  for  evidences  of  steaming. 

(2)  By  noting  the  odor  given  off. 

(3)  By  inserting  an  iron  rod  into  the  pile  and  when  drawn 
out  noting  the  temperature  by  applying  the  hand. 

(4)  By  inserting  maximum  temperature  thermometers  into 
pipes  driven  into  the  pile. 

(5)  By  noting  spots  of  melted  snow  on  the  pile. 

(b)  Water  is  an  effective  agent  in  quenching  fires  in  a coal  pile 
only  if  it  can  be  applied  in  sufficient  quantities  to  extinguish 
the  fire  and  to  cool  the  mass,  but  unless  there  is  an  ample 
supply  for  this  purpose  it  is  dangerous  to  add  any  water  to 
a coal  pile. 

7.  Storage  Systems. — Since  coal  is  a comparatively  cheap  and 
bulky  product,  it  must  be  handled  as  economically  as  possible,  and  also, 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


23 


unless  it  is  to  be  used  in  the  form  of  screenings,  in  a way  to  produce  a 
minimum  of  breakage. 

The  ordinary  power  plant  is  frequently  limited  in  the  choice  of  a 
storage  system  by  a lack  of  available  space  and  by  the  fact  that  ex- 
pense must  be  kept  at  a minimum,  but  it  should  be  recognized  that 
provision  for  storage  may  be  counted  as  an  insurance  against  inter- 
rupted operation.  The  storage  may  be  temporary  or  permanent,  that 
is,  the  coal  may  be  stored  for  use  within  a comparatively  short  time 
or  it  may  be  stored  with  the  expectation  that  it  will  remain  in  storage 
for  a considerable  period  to  serve  as  a reserve  in  case  of  an  emergency, 
the  current  daily  supply  being  used  as  received. 

At  hand  fired  power  plants  coal  is  usually  stored  by  dumping 
or  shoveling  from  a car  or  cart  upon  a pile  or  into  a bin  or  bunker,  or 
merely  by  dumping  upon  the  ground.  From  such  storage  piles  coal 
is  shoveled  directly  into  the  furnace  or,  if  the  pile  is  at  some  distance 
from  the  furnace,  carried  by  wheelbarrow  or  conveyor  to  the  furnace. 

Trestle  storage  involves  the  dumping  of  the  coal  directly  upon 
the  ground  or  into  a bin  from  cars  on  an  elevated  trestle.  Although 
simple  in  construction  and  low  in  first  cost,  trestle  storage  produces 
excessive  breakage  and  unless  drop-bottom  or  dump  cars  are  available 
the  cost  of  unloading  is  high. 

The  cost  of  storing  and  reclaiming  coal  from  storage  by  manual 
labor  varies  from  15  to  64  cents.* 

WARNING: — Special  emphasis  is  laid  upon  the  fact  that  safety 
in  the  storage  of  coal  depends  upon  a very  careful  and  thorough  con- 
sideration of  and  attention  to  the  details  referred  to  in  the  foregoing. 
Lack  of  attention  to  these  details  and  lack  of  care  in  handling  will  in 
many  cases  result  in  losses  due  to  dangerous  fires.  Do  not  undertake 
to  store  coal  until  you  are  sure  you  know  how  to  do  it  properly  and 
safely. 


* Stoek,  H.  H„  “The  Storage  of  Bituminous  Coal.”  CJniv  of  111 
6.  1918. 


Eng.  Exp.  Sta.,  Cxrc 


24 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


III.  The  Combustion  of  Fuel  and  The  Losses 
Attending  Improper  Firing 

8.  Principles  of  Combustion  —The  combustion  of  coal  in  a fur- 
nace is  essentially  a chemical  process.  The  combustible  in  coal  con- 
sists of  carbon,*  hydrogen  and  sulphur.  During  the  progress  of  com- 
bustion these  elements  unite  with  oxygen  to  form  carbon  dioxide, 
steam,  and  sulphur  dioxide  respectively.  The  air,  which  furnishes  the 
oxygen  for  this  process,  consists  of  a mixture  of  21  per  cent  by  volume 
of  oxygen  and  79  per  cent  of  nitrogen.  Oxygen  is  the  active  element 
as  affecting  combustion,  the  nitrogen  being  inert  and  taking  no  part 
in  the  process. 

When  combustion  takes  place,  heat  is  given  off.  For  every  pound 
of  carbon  burned  to  carbon  dioxide,  14,600  B.  t.  u.f  are  released.  In 
the  same  way,  for  every  pound  of  hydrogen  burned  to  water  vapor 
62,100  B.  t.  u.  are  liberated.  One  pound  of  sulphur  in  burning  to 
sulphur  dioxide  gives  up  4,000  B.  t.  u.  The  heat  liberated  serves  to 
raise  the  temperature  of  the  fuel  bed,  of  the  surrounding  surfaces, 
and  of  the  products  of  combustion.  Part  of  the  heat  delivered  to  the 
water  in  the  boiler  is  transmitted  by  direct  radiation  from  the  hot 
surfaces,  and  the  rest  is  absorbed  by  conduction  from  the  gases,  thus 
lowering  their  temperature.  The  heat  carried  away  by  the  gases  after 
they  have  left  the  heating  surfaces  of  the  boiler  represents  the  loss 
entailed  in  the  process.  The  extent  of  this  loss  is,  of  course,  indicated 
by  the  temperature  of  the  gases  leaving  the  heating  surfaces.  The 
nitrogen,  as  stated,  takes  no  part  in  combustion,  but  on  the  contrary 
it  absorbs  a certain  amount  of  heat  in  having  its  temperature  raised 
from  that  of  the  air  to  that  of  the  gases  leaving  the  fire.  Consequently, 
the  temperature  of  the  other  gases  does  not  reach  so  high  a point  as 
would  be  possible  if  oxygen  alone  could  be  introduced  into  the  fuel 
bed.  When  the  nitrogen  leaves  the  heating  surfaces  with  the  rest  of 
the  gases,  it  carries  away  part  of  the  heat  released  by  the  fuel,  and, 

* The  chemical  symbols  used  for  these  elements  and  compounds  are  as  follows:  Carbon 
(O),  hydrogen  (H),  sulphur  (S),  oxygen  (O),  carbon  dioxide  (C02),  steam  (H20),  sul- 
phur dioxide  (S02),  nitrogen  (N),  and  carbon  monoxide  (CO).  Carbon  dioxide  is  variously 
known  as  carbonic  acid  gas  and  as  black  damp,  while  carbon  monoxide  is  known  as  carbonic 
oxide  and  as  white  damp. 

t For  definition  of  B.  t.  u.  see  foot-note  on  page  17. 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


25 


therefore,  represents  loss.  This  loss  amounts  to  about  0.24  B.  t.  u. 
per  pound  of  nitrogen  per  degree  F. 

In  the  process  of  combustion,  one  pound  of  carbon  unites  with 
2.67  pounds  of  oxygen  to  form  3.67  pounds  of  carbon  dioxide.  Since 
the  composition  of  the  air  is  77  per  cent  nitrogen  and  23  per  cent 
oxygen  by  weight,  2.67  pounds  of  oxygen  requires  11.6  pounds  of  air. 

One  pound  of  hydrogen  in  burning  unites  with  eight  pounds  of 
oxygen  to  form  nine  pounds  of  water  vapor.  In  this  case  the  amount 
of  air  required  is  34.8  pounds. 

One  pound  of  sulphur  in  burning  unites  with  one  pound  of  oxygen 
to  form  two  pounds  of  sulphur  dioxide.  The  air  required  is  4.35 
pounds. 

It  is  evident  that  if  the  weights  of  carbon,  hydrogen,  and  sulphur 
in  one  pound  of  coal  are  known,  the  air  necessary  to  burn  completely 
one  pound  of  coal  amounts  to  11.60  times  the  weight  of  carbon,  plus 
34.80  times  the  weight  of  hydrogen,  plus  4.35  times  the  weight  of  sul- 
phur. This  is  about  12  pounds  of  air  per  pound  of  coal.* 

Every  cubic  foot  of  oxygen  used  in  the  combustion  of  carbon  is 
replaced  by  one  cubic  foot  of  carbon  dioxide.  For  this  reason,  the 
percentage  by  volume  of  C02  in  the  flue  gas  is  an  indication  of  the 
amount  of  excess  air  present  in  the  furnace.  A given  amount  of  C02 
will  be  formed  for  every  pound  of  carbon  burned.  If  just  enough  air 
is  used  for  the  complete  combustion  of  the  carbon,  the  oxygen  will  be 
replaced  by  the  C02  formed  and  the  latter  will  be  the  same  percent- 
age, by  volume,  of  the  mixture  as  the  original  oxygen.  If  twice  as 
much  air  as  necessary  is  used,  the  same  volume  of  C02  will  be  formed 
as  before,  but  this  will  replace  only  one  half  of  the  oxygen  used,  and 
hence  its  percentage  of  the  mixture  will  be  only  one  half  as  great  as 
in  the  former  case.  These  relations  are  somewhat  affected  by  the  fact 
that  hydrogen  and  sulphur  are  present,  but  their  amounts  are  too 
small  to  have  an  important  bearing  on  the  result. 

If  less  than  enough  air  is  furnished  for  complete  combustion,  part 
of  the  carbon  in  the  coal,  instead  of  being  burned  to  carbon  dioxide, 
will  form  carbon  monoxide.  Under  these  circumstances  the  amount 
of  heat  liberated  per  pound  of  carbon,  instead  of  being  14,600  B.  t.  u. 
will  be  only  4,500  B.  t.  u.  The  difference,  10,100  B.  t.  u.,  will  represent 
the  heat  lost  for  every  pound  of  carbon  burned  to  carbon  monoxide. 


* Any  air  above  the  chemical  requirement  for  complete  combustion  is  known  as  excess 

air. 


26 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


Since  combustion  is  the  result  of  the  union  of  oxygen  with  the 
various  elements  in  the  coal,  and  with  the  combustible  products  formed 
in  the  fuel  bed,  it  necessarily  follows  that  in  order  to  have  complete 
combustion,  each  particle  of  these  elements  must  come  into  contact 
with  a sufficient  amount  of  oxygen.  To  insure  this  contact  between 
the  particles  of  the  combustible  and  oxygen,  it  is  necessary  to  supply 
an  amount  of  oxygen,  and  hence  of  air,  somewhat  in  excess  of  the 
amount  theoretically  required;  otherwise  carbon  monoxide  will  be 
found  in  the  escaping  gases.  This  excess  acts  as  a further  diluent, 
and  represents  loss,  just  as  the  nitrogen  in  the  air  represents  loss.  A 
compromise  must,  therefore,  be  made.  The  correct  amount  of  air  to 
be  used  is  obtained  when  the  loss  due  to  heating  the  excess  just  bal- 
ances the  loss  due  to  the  carbon  monoxide  appearing  if  the  excess  is 
reduced.  For  best  operating  conditions  it  is  found  necessary  to  use 
between  30  and  40  per  cent  of  excess  air. 

Before  the  union  of  oxygen  and  the  elements  in  the  coal  can  take 
place  with  sufficient  rapidity  to  be  of  any  practical  use,  it  is  necessary 
that -the  whole  mass  be  brought  to  a temperature  known  as  the  igni- 
tion temperature.  If,  because  of  any  condition,  such  as  contact  with 
the  cold  surfaces  of  the  tubes  or  the  inrush  of  an  excessive  amount  of 
cold  air,  the  temperature  of  the  gases  is  lowered  below  the  ignition 
point  before  combustion  is  complete,  combustion  will  cease  and  part 
of  the  fuel  will  escape  from  the  furnace  unburned.  This,  of  course, 
represents  a loss. 

The  three  fundamental  conditions  necessary  for  complete  and 
smokeless  combustion  may  now  be  stated  as  follows : 

(1)  A sufficient  amount  of  air  must  be  supplied. 

(2)  The  air  and  fuel  must  be  intimately  mixed. 

(3)  The  mixture  must  be  brought  to  the  ignition  temperature 
and  maintained  at  this  temperature  until  combustion  is 
complete. 

9.  Significance  of  Draft . — The  technical  meaning  of  the  term 
“draft”  does  not  refer  to  the  motion  of  the  air  or  gases,  but  merely 
defines  the  difference  in  pressure  existing  between  the  air  outside  and 
the  gases  inside  the  furnace  (See  Figs.  3 and  13).  If  there  is  an 
opening  into  the  furnace  and  the  draft  is  maintained,  air  will  be  forced 
in  from  the  outside.  The  amount  of  air  which  passes  will  depend 
upon  the  size  of  the  opening  and  the  resistance  offered  to  the  flow; 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


27 


Fig.  3.  Manometer  Tube  for  Showing  the  Difference  in  Pressure  between 
the  Outside  and  the  Inside  of  a Boiler  Wall 

hence  the  weight  of  air  passing  through  the  fuel  bed  from  the  ash- 
pit for  any  given  draft  over  the  fire  will  depend  upon  the  thickness 
of  the  bed,  the  size  of  the  pieces  of  coal,  and  the  condition  of  the  bed. 
In  any  case,  the  combustion  of  a given  amount  of  coal  always  requires 
a definite  amount  of  air.  Since  for  large  pieces  of  coal  the  voids  in 
the  fuel  bed  are  correspondingly  large,  a fuel  bed  of  given  thickness 
will  present  less  resistance  to  the  passage  of  air  than  a bed  of  finer 
coal  of  the  same  thickness.  Hence  it  requires  less  draft  with  large 
coal  than  with  fine  coal  to  pass  a given  amount  of  air  through  the  fuel 
bed.  It  is,  however,  advisable  to  use  a thicker  bed  with  large  coal  in 
order  to  close  up  the  holes.  This  in  turn  will  make  it  necessary  to  in- 
crease the  draft  to  a point  about  equal  to  that  used  for  fine  coal,  al- 
though the  exact  relation  existing  between  thickness  of  bed,  draft,  and 
load  on  boilers  must  be  determined  by  experiment  in  each  case. 

In  view  of  facts  developed  in  a recent  investigation,*  special  atten- 
tion should  be  given  to  the  regulation  of  the  overdraft  in  hand  fired 
furnaces,  since,  contrary  to  the  generally  accepted  belief,  it  is  shown 

* “Combustion  in  the  Fuel  Bed  of  Hand  Fired  Furnaces,”  by  Henry  Kreisinger,  F. 
K.  Ovitz,  and  C.  E.  Augustine,  Tech.  Paper  No.  137  U.  S.  Bur.  of  Mines,  Washington,  D.  C. 
The  investigation  reported  in  this  publication  discloses  the  following  facts:  “The  current 
of  air  in  passing  through  a uniform  fuel  bed  without  holes  will  have  all  its  oxygen  used 
within  the  first  four  inches  from  the  grate.  The  rate  of  combustion  therefore  varies 
directly  with  the  rate  at  which  air  is  forced  through  a uniform  fuel  bed.  The  completeness 
of  combustion  is  determined  by  mixing  volatile  gases  with  air  in  the  space  above  the  fuel 
bed.  The  reactions  here  are  between  two  gases  rather  than  between  a solid  and  a gas,  and 
the  space  required  for  this  process  is  much  greater.  If  only  the  theoretical  amount  of  air  is 
here  available,  the  mixing  may  not  be  sufficiently  perfected  before  the  gases  have  passed 
out  of  the  combustion  space.  Hence  it  is  necessary  to  supply  an  excess  amount  of  air  over 
the  fuel  bed.  This  air  must  be  introduced  through  openings  above  the  fuel  bed  or  come 
in  through  holes  in  the  fire.” 


28 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


that  most  of  the  excess  air  is  admitted  into  the  combustion  chamber 
above  the  fuel  bed  instead  of  through  the  fuel  bed. 

Every  boiler  should  be  equipped  with  two  draft  gages,  one  con- 
nected directly  into  the  space  over  the  fire  (Fig.  4),  and  one  connected 


Fig.  4.  Sketch  Showing  the  Correct  Method  of  Connecting  Draft  Gages 

both  into  the  space  over  the  fire  and  into  the  gas  passage  below  the 
damper,  giving  the  drop  in  pressure  through  the  tubes  and  baffling. 
The  operation  of  the  boilers  should  be  controlled  by  means  of  the  draft 
over  the  fire.  The  draft  necessary  to  carry  any  given  load  and  the 
corresponding  proper  thickness  of  fuel  bed  with  the  grade  of  coal  used 
should  be  determined.  With  everything  in  good  shape  and  no  leaks 
in  the  setting  and  a given  draft  over  the  fire,  there  should  be  a definite 
loss  of  draft  through  the  setting,  or  differential  draft  as  it  will  herein- 
after be  called.  When  the  damper  is  opened  to  increase  capacity,  both 
the  furnace  draft  and  the  differential  draft  will  increase.  Assuming 
that  the  correct  thickness  of  fuel  bed  is  being  used,  an  increase  in  the 
differential  draft  reading  over  the  normal  reading  with  the  given 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


29 


furnace  draft  indicates  that  there  are  holes  in  the  fuel  bed  or  that  the 
tubes  have  become  clogged  with  soot  and  ash.  A decrease  in  the  dif- 
ferential draft  indicates  that  the  fuel  bed  is  dirty  and  that  the  resist- 
ance is  greatly  increased  by  ash  or  clinker,  or  that  some  of  the  baffling 
is  down,  causing  a short  circuit  of  the  gases. 

10.  Significance  of  C02  in  the  Flue  Gases. — A study  of  the 
amount  of  carbon  dioxide  (C02)  in  the  flue  gases  affords  the  only 
practical  means  of  obtaining  a knowledge  of  conditions  existing  with- 
in the  furnace  on  the  basis  of  which  correction  or  regulation  to  obtain 
the  best  results  may  be  made.  The  importance  of  making  C02  determi- 
nations, therefore,  warrants  a discussion  of  the  methods  by  which 
these  determinations  may  be  made.  Every  plant  should  be  equipped 
with  some  form  of  C02  analyzing  apparatus  and  the  fireman  or  other 
employe  taught  to  use  it.  Since  it  is  comparatively  inexpensive,  the 
outlay  will  be  returned  many  times  by  the  gain  in  efficiency  and  the 
consequent  saving  of  fuel.  For  this  purpose  an  Orsat  apparatus  or 
some  of  its  modified  forms  should  be  used.  The  complete  Orsat  ap- 
paratus provides  a means  of  analyzing  for  carbon  dioxide,  oxygen,  and 
carbon  monoxide,  but  since  the  C02  values  give  a sufficiently  accurate 
indication  of  the  amount  of  excess  air  passing  through  the  fire,  the 
analysis  for  the  other  two  gases  may  be  omitted  and  the  apparatus 
used  in  its  simplest  form,  as  shown  in  Fig.  5.  This  consists  merely  of 
of  a pipette,  h,  to  hold  the  solution  (potassium  hydroxide),  a measur 
ing  burette,  e,  of  100  cubic  centimeters  capacity,  a leveling  bottle,  /, 
containing  water,  and  an  aspirating  bulb,  m.  The  solution  may  be 
made  by  mixing  equal  weights  of  potassium  hydroxide  (KOH)  and 
water.  In  the  absence  of  this  chemical,  concentrated  lye  may  be 
used. 

In  using  the  C02  apparatus,  the  liquid  in  the  pipette,  h,  is  first 
brought  to  the  mark,  o,  just  below  the  cock,  d.  This  can  be  done 
by  lowering  the  leveling  bottle,  f,  after  which  the  cock,  d,  should  be 
closed.  The  3-way  cock,  c,  is  then  opened  to  the  burette,  e,  and  to 
h,  and  by  raising  the  leveling  bottle,  /,  the  water  in  the  burette  is 
brought  to  the  mark,  g,  and  the  cock,  c,  closed  to  the  burette,  and 
opened  through  a and  h.  The  aspirating  bulb,  m,  is  now  worked, 
drawing  gas  from  the  sample  tube,  n,  in  the  setting  and  forcing 
it  out  through  h.  When  sufficient  gas  has  been  forced  through  to 
clean  out  the  air  and  dead  gas  from  the  sample  tube,  the  cock,  c,  is 


30 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


turned  so  that  b is  closed,  and  a is  in  communication  with  the 
burette,  e.  The  sample  is  then  pumped  into  the  burette,  thus  driv- 
ing the  water  into  the  leveling  bottle  and  more  than  filling  the 
burette.  The  leveling  bottle  is  then  raised  until  the  water  in  the 


burette  stands  exactly  at  100  cc.,  the  rubber  tubing  between  the 
leveling  bottle  and  the  burette  is  clamped  between  the  thumb  and 
finger  so  that  no  change  in  the  level  at  100  cc.  can  take  place  and  the 
cock,  c,  momentarily  opened  to  the  atmosphere  through  b and  then 
closed  to  the  burette.  If  this  has  been  done  correctly,  when  the  two 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


31 


surfaces,  e and  /,  are  brought  to  the  same  level,  e should  stand  at 
100  cc.  An  alternate  method  of  obtaining  100  cc.  at  atmospheric 
pressure  is  to  have  the  3-way  cock  open  through  a to  c and  closed  to 
b.  The  gas  may  now  be  forced  out  through  the  liquid  in  the  leveling 
bottle,  /.  The  water  -at  / and  e may  now  be  brought  to  the  same 
level  and  the  cock  closed  to  the  burette,  e.  The  cock,  d,  is  now 
opened  and  the  gas  driven  into  the  pipette,  h,  by  raising  the  level- 
ing bottle.  It  should  be  driven  back  and  forth  between  the  burette 
and  pipette  several  times,  and  then  the  liquid  in  the  pipette  brought 
back  to  the  mark,  o,  and  the  cock,  d,  is  closed.  The  surfaces,  / and 
e,  are  again  brought  to  the  same  level,  and  the  amount  of  C02  in 
the  gas  sample  is  read  from  the  burette  at  e.  This  operation  is 
easily  performed  and  a fireman  of  ordinary  intelligence  can  analyze 
a sample  in  about  two  minutes. 

There  are  several  precautions  which  should  be  observed  in  tak- 
ing samples.  There  must  be  no  leaks  in  the  rubber  tubing  or  con- 
nections. If  air  leaks  in  during  the  analysis,  it  invalidates  the 
result.  The  sole  object  in  making  an  analysis  is  to  determine 
what  the  fire  is  doing  at  the  time  the  sample  is  taken;  hence  the 
apparatus  should  be  hung  on  the  setting  at  a point  as  near  as  possible 
to  the  point  where  the  sample  is  taken  in  order  to  reduce  the  amount 
of  piping  and  rubber  tubing  between  the  sampling  tube  and  the 
analyzer,  and  to  insure  a sample  representative  of  conditions  at 
the  time.  If  the  sample  is  conveyed  through  tubes  of  considerable 
size  and  length,  as  is  usually  the  case  with  a C02  recorder  or  even  with 
a C02  indicator,  the  analysis  is  made  from  5 to  15  minutes  after  the 
sample  is  taken.  Thus  a hole  in  the  fire  may  be  disclosed  by  the 
analyzer  5 or  10  minutes  after  its  initial  occurrence  and  even  after  its 
disappearance  by  filling  up.  The  C02  recorder,  therefore,  is  useful 
for  giving  an  idea  of  the  average  operation  over  a long  period,  but 
is  not  satisfactory  as  a means  of  determining  the  proper  relation 
between  load,  draft,  fuel  bed  thickness,  and  other  conditions.  The 
determination  of  such  relations  involves  simultaneous  readings. 

Precautions  must  be  observed  in  inserting  the  sampling  tube. 
An  elaborate  sampling  apparatus  used  in  the  hope  of  obtaining  an 
average  sample  is  not  to  be  recommended.  Such  apparatus  consists 
mainly  of  a double  tube  arrangement  having  a series  of  small 
holes  drilled  into  the  tubes,  the  tubes  extending  across  the  gas 
passage.  These  do  not  accomplish  the  desired  result,  however,  be- 


32 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


cause  the  holes  become  clogged  with  soot  and  ash  making  it  impossible 
to  know  the  point  in  the  flue  from  which  the  sample  is  drawn. 
Another  reason  why  these  tubes  are  not  reliable  for  procuring  an 
average  sample  lies  in  the  fact  that  the  gas  stream  varies  across  the 
flue  in  all  directions,  while  the  sampling  tubes  can  at  best  give  an 
average  in  only  one  direction.  In  order  to  obtain  an  exact  average 


Fig.  6.  Sketch  Showing  the  Proper  Location  for  Gas  Sampling  Tubes  to 
Avoid  Damper  Pockets  for  Both  Front  and  Rear  Take-off 

Point  2 is  in  the  center  of  the  main  gas  stream  and  indicates  correct  position  of  the  sampling 
tube.  Points  1 and  3 show  locations  of  pockets  in  which  representative  samples 
cannot  be  secured. 

it  would  be  necessary  to  fill  the  flue  with  a network  of  sampling 
tubes  so  arranged  that  each  might  take  a quantity  of  gas  propor- 
tional to  the  velocity  of  the  stream  at  its  point  of  sampling.  For 
all  practical  purposes,  therefore,  it  is  best  to  take  a sample  through 
the  end  of  a straight  tube  consisting  of  a piece  of  ^-incli  pipe  so 
that  the  point  of  sampling  may  be  known  with  accuracy.  A sample 
taken  from  the  center  of  the  main  gas  stream  where  the  gas  lias 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


33 


the  greatest  velocity  has  been  found  to  yield  an  accurate  indication 
of  the  condition  of  the  fuel  bed  at  the  time  of  sampling,  slight  vari- 
ations in  the  condition  of  the  fire  being  reflected  immediately  in 
the  sample.  In  placing  the  tube,  care  should  be  taken  to  have  the 
end  in  the  center  of  the  main  gas  stream  at  point  No.  2,  Fig.  6,  and 
not  in  any  of  the  dead  gas  pockets  as  indicated  by  points  1 and 
3.  Otherwise  low  C02  values  not  representative  of  the  actual  con- 
ditions will  be  obtained.  The  tube  should  be  inserted  at  the  point 
where  the  gases  leave  the  heating  surfaces  of  the  boiler  for  the  last 
time  as  indicated  by  point  2 in  Fig.  6,  and  not  further  out  in  the 
flue.  An  iron  tube  should  not  be  used  if  the  temperature  at  the 
point  of  sampling  is  sufficient  to  raise  it  to  a red  heat,  because  the 
character  of  the  sample  may  be  affected  by  part  of  the  oxygen  in 
the  sample  uniting  with  the  red  hot  iron.  A small  cotton  filter,  con- 
tained in  a glass  tube,  should  be  inserted  between  the  sampling  tube 
and  the  aspirator  bulb.  In  using  the  apparatus  shown  on  page  30, 
care  should  be  taken  to  prevent  a draft  of  cold  air  striking  the  burette 
during  a reading.  A material  change  in  temperature  during  a reading 
will  invalidate  the  result. 

11.  Losses  of  Heat  Value. — The  losses  in  the  boiler  plant  may 
be  divided  into  two  classes: 

(1)  Those  due  to  the  loss  of  green  coal  in  handling. 

(2)  Those  resulting  in  the  process  of  combustion.  Losses 

of  the  first  class  are  usually  small  and  easily  detected ; hence 
they  will  not  be  discussed  further. 

The  principal  losses  are  those  entailed  in  the  process  of  com- 
bustion. These  may  be  divided  into  the  following  classes : 

(1)  Loss  due  to  excess  air  and  air  leakage  through  the  setting. 

(2)  Loss  due  to  combustible  in  ash. 

(3)  Loss  due  to  C02  formed. 

(4)  Loss  due  to  soot  on  the  tubes. 

(5)  Loss  due  to  moisture  carried  in  with  the  coal  and  air. 

(6)  Loss  due  to  heat  carried  out  by  the  escaping  gases. 

(7)  Loss  due  to  radiation. 

Losses  included  under  classes  1 to  4,  inclusive,  are  largely  pre- 
ventable, while  those  under  classes  5,  6 and  7 are  more  or  less  inevit- 
able, although  they  may  be  reduced  to  a minimum  with  proper  care. 


34 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


Excess  Air  and  Air  Leaks 

Losses  due  to  excess  air  and  to  air  leaks  are  discussed  together 
because  they  may  both  be  detected  by  the  same  means,  i.  e.,  by  analysis 
of  the  flue  gas.  Under  the  head  of  excess  air  may  be  included  all  air 
which  goes  through  the  combustion  zone  in  excess  of  the  amount 
required  for  perfect  combustion.  Air  leakage  includes  all  air  going 
through  holes  in  the  setting  and  other  places  besides  the  fuel  bed. 

The  space  inside  the  average  boiler  setting  is  at  less  than  atmos- 
pheric pressure;  hence  if  there  are  any  openings  in  the  setting,  air 
will  leak  through  from  the  outside.  This  cold  air  not  only  takes  no 
part  in  the  combustion,  but  its  temperature  must  be  raised  to  that 
of  the  rest  of  the  gas,  a process  which  requires  heat  and  lowers  the 
temperature  of  the  other  gases.  Some  of  this  heat  is  given  back  to  the 
water  in  the  boiler,  but  all  that  indicated  by  the  difference  between 
the  temperature  of  the  flue  gas  and  that  of  the  air  in  the  boiler  room 
represents  a dead  loss.  This  is  also  true  of  the  excess  air  carried 
through  the  fuel  bed.  While  these  losses  cannot  be  detected  with  the 
naked  eye,  like  that  due  to  green  coal  in  the  ash,  they  are  by  far  the 
most  serious  of  all  losses  occurring  in  the  average  plant. 

Leaks  in  the  setting  may  occur  in  the  metal  work  around  doors 
and  joints  as  well  as  in  the  brickwork.  When  leaks  are  found  they 
should  not  only  be  stopped  with  asbestos  or  stove  putty,  but  should 
be  calked  with  waste  or  asbestos  fiber  soaked  with  fireclay  in  such 
manner  as  to  prevent  cracking  off  or  falling  out  as  soon  as  dry. 
The  last  of  the  leaks  may  best  be  found  by  building  a smoky  fire 
and  shutting  the  damper.  Smoke  may  then  be  seen  to  issue  where- 
ever  there  is  a leak.  When  the  setting  has  been  made  as  tight  as 
possible,  air  will  still  seep  in  because  the  bricks  and  the  mortar  are 
porous.  This  leakage  may  be  reduced  to  a minimum  by  tacking  metal 
lath  to  the  setting  and  applying  a coat  of  plaster  one  inch  or  so  in 
thickness  made  of  a mixture  of  about  80  per  cent  magnesia  and  20 
per  cent  old  magnesia  pipe  covering.  In  order  to  secure  a satisfac- 
tory surface  85  per  cent  magnesia  should  be  mixed  with  cement  to 
form  a thin  grout,  spread  on  the  surface,  troweled  to  a smooth  finish, 
and  painted.  This  makes  a good  lagging  not  affected  by  temperature 
changes  and  also  serves  to  reduce  the  radiation  loss  listed  under  class 
(7).  If  the  setting  is  too  hot  to  permit  touching  it  with  the  hand 
without  discomfort,  the  radiation  loss  is  excessive. 

After  the  setting  has  been  made  absolutely  tight  it  will  pay  to 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


35 


give  attention  to  the  excess  air  loss,  but  it  is  well  to  emphasize 
that  the  former  should  be  done  first.  There  exists  a very  definite 
relation  between  capacity,  draft,  fuel  bed  thickness,  and  air  passing 
through  the  fuel  bed  with  a given  grade  of  coal.  For  Illinois  coal 
a draft  of  approximately  .01  inch  of  water  is  required  to  burn  one 
pound  of  coal  per  square  foot  of  grate  surface  per  hour.  This  ratio 
is  slightly  increased  for  rates  of  combustion  above  twenty-five  pounds 
of  coal  per  square  foot  per  hour. 

In  order  to  determine  these  relations  in  any  given  plant,  a time 
should  be  chosen  when  the  load  on  the  boilers  will  remain  constant 
for  several  hours.  The  fire  should  be  clean,  of  uniform  thickness, 
and  free  of  holes,  and  the  surfaces  of  the  tubes  should  be  free  of  soot. 
A draft  and  fuel  bed  thickness  sufficient  to  maintain  the  load  without 
loss  of  pressure  should  then  be  chosen.  Simultaneous  readings  of  the 
draft  and  analyses  of  the  flue  gas  should  now  be  made  as  rapidly 
as  possible  and  repeated  at  brief  intervals  to  insure  permanence  of 
conditions,  and  a watch  should  be  kept  on  the  fire  to  see  that  holes 
do  not  develop.  Care  must  be  taken  not  to  open  the  furnace  doors 
during  a reading.  Records  should  be  kept  of  the  drafts,  C02,  and 
fuel  bed  thickness.  Thickness  of  fuel  bed  should  then  be  varied  and 
the  draft  adjusted  to  carry  the  load  without  pressure  drop,  or 
without  blowing  the  safety  valves.  When  sufficient  time  has  elapsed 
to  allow  conditions  to  become  constant,  another  set  of  readings 
should  be  taken.  If  too  thin  a fuel  bed  were  used  at  the  start,  it  will 
be  found  on  comparing  the  readings  that  as  the  thickness  of  the  fuel 
bed  is  increased,  the  draft  increases,  and  the  percentage  of  C02  also 
increases.  Finally  a point  will  be  reached  at  which  the  C02  does  not 
increase  further  as  the  thickness  of  the  fuel  bed  and  the  draft  increase. 
The  draft  and  fuel  bed  thickness  to  give  this  C02  reading  represent  the 
proper  values  for  the  given  load  on  the  boiler,  under  which  the  suggested 
changes  in  operating  conditions  have  been  made.  This  process  should 
then  be  repeated  for  a number  of  different  loads  on  the  boiler.  Upon 
doing  this  it  will  be  found  that  with  a given  thickness  of  fuel  bed, 
certain  more  or  less  well  defined  limits  of  draft  over  the  fire  will 
give  a maximum  C02  reading.  The  draft  then  becomes  the  key  for 
controlling  the  whole  situation.  If  the  load  on  the  boiler  is  such  as 
to  require  drafts  between  certain  limits,  then  the  thickness  of  fire 
which  should  be  used  is  immediately  known,  provided  there  are  no 
holes  in  the  fire  and  the  tubes  and  fire  are  clean.  These  latter 


36 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


conditions  will  be  indicated  by  the  differential  draft  gage,  Fig.  4, 
readings  of  which  should  also  have  been  taken  during  the  tests  when 
the  tubes  were  known  to  be  clean  and  the  fire  in  good  condition.  A 
table  or  chart  should  be  laid  out  for  the  use  of  the  fireman,  which, 
as  soon  as  the  approximate  draft  necessary  to  maintain  boiler  pres- 
sure is  known,  gives  the  thickness  of  fire  to  be  carried  and  the  cor- 
responding differential  draft  gage  reading.  If  the  furnace  draft 
and  thickness  of  fire  are  correctly  maintained  and  the  differential 
is  then  too  low,  it  indicates  either  that  the  fire  is  dirty  or  that  some 
of  the  baffling  has  fallen.  A too  high  reading  of  the  differential 
indicates  that  there  are  holes  in  the  fire,  or  that  soot  is  clogging  the 
passages  through  the  tubes. 

The  thickness  of  the  fire  should  not  be  left  to  the  judgment 
of  the  fireman,  but  definite  marks  should  be  placed  on  the  inside 
door  liners,  or  at  some  points  where  they  may  be  seen.  In  any 
case,  it  should  be  thoroughly  understood  that  the  cooperation  of 
the  fireman  is  necessary,  and  unless  the  fires  are  kept  clean,  and 
the  firing  is  done  in  such  manner  as  to  maintain  a uniform  fuel  bed 
without  holes  the  other  precautions  suggested  are  useless. 

Since  air  leakage  through  the  setting  tends  to  increase  as  the 
draft  increases,  it  is  good  policy  to  run  on  the  mi  minium  draft  which 
will  carry  the  load  without  pressure  drop.  The  C02  readings  are  a 
direct  indication  of  the  total  loss  due  to  both  excess  air  and  to  air 
leakage  when  taken  just  below  the  damper.  A curve  # is  presented 
in  Fig.  7 which  has  been  plotted  from  flue  gas  readings  when 
burning  Illinois  slack  on  a chain  grate.  It  gives  the  percentage  of 
excess  air  represented  by  different  percentages  of  C02  in  the  gas. 
From  this  curve  it  may  be  seen  that  12  per  cent  of  C02  represent 
about  35  per  cent  excess  air.  This  is  the  maximum  C02  reading 
obtainable  with  this  coal  when  burned  on  grates  of  approximately 
93  per  cent  grate  efficiency  without  danger  of  incomplete  combus- 
tion and  a corresponding  loss  due  to  carbon  monoxide.  If  this  value 
is  not  exceeded,  it  will  not  be  necessary  to  analyze  for  carbon  monox- 
ide and  the  determination  for  C02  is  sufficient. 

It  has  been  mentioned  in  a preceding  paragraph  that  the  proper 
position  for  the  sampling  tube  is  at  a point  where  the  hot  gases  leave 
the  heating  surfaces  for  the  last  time.  The  reason  for  this  may  now 


* Kratz.,  A.  P.,  “A  Study  of  Boiler  Losses.”  Qniv.  of  111.  Eng.  Exp.  Sta.,  Bui.  78, 
p.  33,  1915. 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


37 


be  made  clear.  The  C02  in  the  sample  at  this  point  is  an  indication 
of  all  the  excess  air  and  leakage  which  has  diluted  the  gas  and 
absorbed  heat  which  should  have  gone  into  the  water.  After  the 
gases  leave  the  heating  surfaces  there  is  no  longer  any  chance  of 
heat  being  absorbed  and  it  is  not  important,  so  far  as  efficiency  is 
. concerned  whether  it  is  lost  in  a small  amount  of  gas  at  a high  tem- 


Percent  excess  a/r 

Fig.  7.  Curve  Showing  Relation  between  Excr  Air  and  C02  in  Flue  Gas 
(See  “A  Study  of  Boiler  Losses,’ ’ Univ.  of  111.  F Exp.  Sta.,  Bui.  78,  1915.) 

perature,  or  in  a large  amount  of  air  and  g t a lower  temperature. 
Any  air  leakage  beyond  this  point,  there  l-.  e,  does  not  lower  the 
efficiency.  The  harmful  effect,  however,  h shown  on  the  capacity. 
It  not  only  adds  its  own  bulk  to  the  gases  tl  ? chimney  must  carry, 
but  also,  due  to  its  cooling  effect  on  the  ho  ^ases,  lessens  the  draft 
available  to  produce  the  flow.  In  many  case  , the  mere  stopping  of 
the  leaks  in  setting  and  breeching  has  enable  ' toilers  to  carry  over- 
load, while  previously  it  had  been  impossible  i.  oAain  rated  capacity. 

The  draft  should  be  controlled  by  meaiu-  of  the  dampers  at  the 
flue,  and  not  by  the  ashpit  doors.  Closing  the  ashpit  doors  prevents 
air  from  going  through  the  fuel  bed,  causes  cum  er  and  hot  grates, 


38 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


and  also  increases  the  air  leakage  loss.  Each  boiler  should  be 
equipped  with  a separate  damper  and  the  position  of  maximum  and 
minimum  damper  opening  should  be  determined.  The  damper  should 
then  be  operated  between  these  limits.  The  points  of  maximum  and 
minimum  opening  should  be  found  by  noting  the  reading  of  the  draft 
gage  while  the  damper  is  moved  from  one  extreme  position  to  the 
other.  These  points  of  maximum  and  minimum  draft  gage  reading 
may  not  coincide  with  the  points  at  which  the  damper  is  mechani- 
cally open  or  closed.  A position  will  usually  be  found  at  which  the 
draft  is  maximum,  and  a further  opening  of  the  damper  will  not 
change  the  reading.  It  may  also  be  found  that  the  damper  can  be 
opened  quite  appreciably  before  the  draft  gage  begins  to  read. 
In  many  plants  of  large  and  medium  size  automatic  draft  control 
has  proved  economical  and  it  is  also  of  advantage  in  maintaining 
constant  steam  pressure.  If  automatic  control  of  the  draft  is  used, 
it  is  important  to  have  the  damper  adjusted  for  the  range  of  travel 
determined  by  experiment  as  suggested,  so  that  the  draft  will  be 
proportional  to  the  opening.  An  automatic  damper  regulator,  when 
used,  should  preferably  be  of  the  type  which  responds  to  small 
decreases  or  increases  in  steam  pressure  by  causing  a corresponding 
movement  of  the  damper,  and  not  of  the  type  which  either  com- 
pletely opens  or  completely  closes  the  damper  in  response  to  small 
decreases  or  increases  of  pressure.  If  there  are  several  boilers  in 
the  plant,  the  best  plan  is  to  adjust  the  individual  dampers  so  that 
each  boiler  is  carrying  its  share  of  the  load  under  the  most  economi- 
cal draft,  and  then,  if  the  total  load  changes,  to  regulate  with  a 
master  damper  in  the  main  flue. 

Loss  Due  to  the  Presence  of  Combustible  in  the  Ash 
The  loss  due  to  partly  burned  coal  in  the  ash  should  not,  with 
very  careful  handling  of  the  fire,  exceed  more  than  about  three  per 
cent  of  the  heat  value  of  the  coal.  Excessive  carbon  in  the  ash  with 
stoker  fired  furnaces  usually  indicates  too  rapid  feed  for  the  rate 
of  combustion  used.  In  hand  fired  furnaces  it  may  indicate  that  the 
grate  openings  are  too  large  for  the  size  of  coal  used  or  that  the  fire 
is  worked  too  much,  or  both.  So  far  as  possible  the  fire  should  be 
operated  without  much  working  except  at  times  of  cleaning.  Too 
much  working  does  two  things;  first,  it  shakes  the  green  coal  down 
into  the  ash  and  allows  it  to  pass  through  the  grate  bars,  and 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


39 


secondly,  it  brings  the  ash  up  into  the  hot  part  of  the  fire  where  it 
fuses  and  causes  clinker.  Partly  burned  coal  is  fused  in  with  the 
clinker  and  is  lost  when  the  clinker  is  removed,  and  the  coal  which 
is  shaken  through  the  grates  during  the  additional  working  required 
to  remove  the  clinker  adds  further  to  the  loss.  The  possible  loss 
due  to  firing  green  coal  into  holes  in  the  fire  and  thus  permitting  it 
to  pass  through  the  grate  has  not  been  considered  in  detail  because 
it  is  obvious  that  the  holes  should  be  filled  up  by  leveling  the  fire 
before  adding  a fresh  charge  of  green  coal.  In  working  a fire,  it  should 
be  sliced  from  the  bottom  in  such  a manner  as  to  avoid  or  minimize 
the  possibility  of  forcing  ash  up  into  the  fuel  bed.  This  applies  to 
stoker  firing  as  well  as  to  hand  firing. 

Loss  Due  to  the  Presence  of  Carbon  Monoxide 

in  the  Flue  Gases 

Carbon  monoxide  is  formed  if  too  thick  a fire  or  an  insufficient 
draft  is  used.  With  central  bituminous  coals  there  is  little  possibility 
of  large  loss  from  this  source  if  the  C02  reading  is  not  more  than  12 
per  cent. 

Loss  Due  to  Soot 

The  largest  part  of  the  loss  due  to  smoke  does  not  result  from 
the  fact  that  the  particles  of  carbon  floating  in  the  gas  stream  have 
passed  out  before  giving  up  their  heat  value,  but  it  comes  from  the 
deposit  of  soot  on  the  tubes.  The  actual  heat  value  of  this  deposit  of 
soot  is  small  when  compared  with  the  amount  of  coal  fired  in  pro- 
ducing it,  but  its  power  of  preventing  the  heat  in  the  gases  from 
reaching  the  tubes  and  being  absorbed  is  a factor  of  considerable 
importance.  Soot  makes  an  excellent  heat  insulator,  about  five  times 
as  effective  as  asbestos.  Under  normal  working  conditions  and  with 
the  normal  amount  of  air,  the  temperature  of  the  gases  leaving  the 
boiler  should  be  somewhere  near  550  degrees  F.  If  they  leave  at  a 
much  higher  temperature  and  the  fire  and  drafts  are  normal,  it 
signifies  that  the  tubes  need  blowing.  The  soot  deposited  on  the 
heating  surfaces  is  keeping  the  heat  in  the  gas  from  reaching  the 
water  and  the  gases  consequently  are  not  cooled.  Where  automatic 
blowers  are  installed  the  tubes  should  be  blown  every  four  or  five 
hours.  In  all  cases  they  should  be  blown  at  least  once  for  every  shift. 
A pyrometer  placed  at  the  point  where  the  gases  leave  the  tubes 
for  the  last  time  will  give  a fairly  good  indication  of  their  condition, 
provided  of  course  that  low  temperature  is  not  due  to  excess  air. 


40 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


Loss  Due  to  Moisture  in  the  Coal  and  Air 
The  loss  due  to  moisture  in  the  air  is  very  small  and  need  not  be 
considered.  That  due  to  moisture  in  the  coal  may  be  larger.  The 
coal  may  carry  13  or  14  per  cent  of  moisture,  and  the  heat  required 
to  evaporate  this  must  be  furnished  by  the  coal  itself,  thus  decreasing 
the  amount  available  to  heat  water  in  the  boiler.  Fine  coal  tends  to 
pack  if  fired  dry.  This  prevents  the  proper  amount  of  air  getting 
to  the  fuel,  and  results  in  the  formation  of  carbon  monoxide  and  in 
cold  fires.  Sometimes  very  dry  coal  burns  out  unevenly,  and  will 
not  stay  on  the  grates  without  allowing  holes  to  form.  For  these 
reasons,  it  is  advisable  to  wet  down  the  smaller  sizes  of  coal  just 
before  firing  because  the  other  losses  mentioned  are  greater  than 
that  due  to  the  water.  With  larger  sizes  wetting  is  not  necessary  and 
is  not  advisable.  This,  however,  must  be  decided  for  each  individual 
plant.  In  no  case  should  more  water  be  added  than  is  absolutely 
necessary. 


Loss  Due  to  Heat  in  the  Escaping  Gases 

Every  pound  of  flue  gas  passing  up  the  stack  represents  a loss 
of  about  .24  heat  units  per  degree  F.  above  the  temperature  of  the 
steam  in  the  boiler.  This  loss  cannot  be  entirely  eliminated.  For 
plants  operating  on  natural  draft,  a temperature  of  about  500  degrees 
F.  is  required  in  the  stack  to  produce  the  draft  necessary  to  operate 
the  boilers  at  full  capacity.  An  average  of  550  degrees  F.  is  good 
practice.  For  forced  draft  and  four-pass  boilers,  it  may  run  lower 
than  this  temperature.  An  indicating  pyrometer  should  be  used  on 
each  boiler  and  if  the  temperature  in  the  flue  becomes  abnormally 
high  it  may  be  accepted  as  an  indication  of  an  excessive  deposit  of 
soot  upon  the  tubes  or  of  a draft  greater  than  is  necessary  for  the 
load. 

Loss  Due  to  Radiation 

Uncovered  surfaces  and  other  surfaces  which  are  too  hot  to  touch 
without  discomfort  represent  a serious  loss  of  heat.  This  loss  can  be 
decreased  by  covering  the  setting  as  previously  suggested. 

12.  Significance  of  Smoke. — Smoke,  depending  upon  its  cause, 
may  or  may  not  indicate  a loss  in  efficiency.  The  loss  is  largely  due 
to  the  soot  deposit,  and  not  to  the  heat  value  of  the  fine  particles 
of  floating  carbon.  The  three  principles  of  smokeless  combustion 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


41 


have  already  been  stated.  The  question  concerning  whether  there  is 
sufficient  air  for  combustion  can  be  answered  with  the  C02  analyzer. 
If  the  C02  reading  is  normal  and  smoke  still  appears,  the  trouble  is 
due  either  to  a faulty  mixture  of  the  air  and  combustible  gases,  or 
to  a too  small  combustion  chamber.  Increasing  the  air  supply  may 
decrease  the  smoke,  but  it  also  decreases  the  efficiency.  In  this  case 
smokeless  combustion  does  not  indicate  high  efficiency.  If  the  fire  is 
hot  and  there  is  much  oxygen  in  the  gas,  together  with  high  carbon 
monoxide,  the  trouble  is  due  to  poor  mixing  of  the  gas  and  air  over 
the  fuel  bed.  Mixing  piers  or  arches  will  eliminate  the  smoke  which 
in  this  case  is  an  indication  of  loss  of  efficiency.  If  the  fire  is  white 
hot,  and  the  C02  normal,  without  any  indication  of  carbon  monox- 
ide in  the  gas  the  trouble  is  due  to  a too  small  combustion  chamber. 
In  most  plants  this  is  the  cause  of  smoke,  and  in  such  cases  it  does 
not  indicate  poor  furnace  efficiency.  The  loss  is  due  to  soot  rather 
than  to  smoke. 

13.  Methods  of  Hand  Firing. — There  are  two  general  methods 
advocated  for  hand  firing,  (1)  Coking,  (2)  Spreading.  The  first 
involves  the  placing  of  a considerable  amount  of  green  coal  on  some 
convenient  part  of  the  fuel  bed  where  the  heat  will  pass  into  it  and 
will  slowly  distil  the  volatile  gases.  These  gases  then  mix  with  air 
above  the  bed  and  in  passing  over  the  white  hot  bed  are  burned 
before  they  reach  the  cold  surfaces.  The  method  usually  adopted  is 
to  pile  the  green  coal  at  the  front  of  the  bed.  After  10  or  15  minutes, 
during  which  the  coal  has  become  well  coked,  this  pile  is  broken  up  and 
spread  over  the  back  part  of  the  fuel  bed,  and  a fresh  charge  is  piled 
at  the  front.  This  method  accomplishes  satisfactory  results  so  far 
as  smokeless  combustion  is  concerned,  but  it  does  not  promote 
efficiency.  The  keynote  of  efficiency  lies  in  the  maintenance  of  a 
uniform  fuel  bed,  while  with  the  coking  method  of  firing  the  bed 
burns  unevenly.  The  bed  is  usually  too  thick  at  the  front,  and  burns 
out  and  develops  holes  at  the  rear,  and  although  it  is  less  liable  to  form 
clinker,  this  practice  is  not  to  be  recommended  as  highly  as  some 
form  of  spreading. 

In  the  spreading  method,  small  quantities  of  coal  are  fired  at 
frequent  intervals.  In  alternate  spreading,  a thin  layer  of  coal  is 
spread  on  one  side  of  the  furnace.  As  the  gases  distil,  they  mix  with 
the  air,  and  the  white  hot  surface  on  the  other  side  maintains  the 


42 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


mixture  at  the  ignition  temperature.  After  a period  of  about  five 
minutes,  when  the  distillation  is  complete,  another  charge  of  fresh 
coal  may  be  spread  on  the  other  side  of  the  bed.  By  this  method  the 
fire  may  be  kept  in  a more  nearly  uniform  condition  than  by  coking. 
Where  the  coal  is  spread  over  any  considerable  area,  however,  there 
is  still  a tendency  for  the  resistance  at  different  parts  to  vary,  and 
for  holes  to  develop. 

The  best  method  is  to  fire  very  often  and  in  small  quantities. 
Holes  should  not  be  permitted  to  develop ; to  prevent  holes,  small 
amounts  of  coal  should  be  placed  on  the  thin  parts  of  the  bed.  Thin 
places  may  be  recognized  from  the  fact  that  they  appear  brighter 
and  hotter  than  the  rest  of  the  bed.  This  method  requires  more 
attention  on  the  part  of  the  fireman,  but  it  pays  in  the  long  run.  It 
is  possible  to  maintain  a uniform  bed  for  long  periods  without  barring 
or  working  the  fire.  Where  the  coal  is  fired  in  small  quantities,  the 
volume  of  combustible  distilled  at  one  time  is  small  and  may  be 
easily  consumed  over  the  hot  part  of  the  fuel  bed  without  forming 
smoke. 

In  any  case,  in  hand  firing,  it  is  necessary  that  some  auxiliary 
air  be  taken  in  over  the  fuel  bed  for  several  minutes  immediately 
after  firing.  This  should  be  admitted  across  the  fire  close  to  the 
surface  of  the  fuel  bed,  preferably  from  the  front  through  auxil- 
iary dampers  in  the  fire  door,  which  should  have  an  area  of  at  least 
four  square  inches  per  square  foot  of  grate  surface.  This  admission 
of  air  may  be  accomplished  either  automatically  or  under  the  control  of 
the  fireman.  The  automatic  device  opens  small  supplementary  damp- 
ers when  the  fire  door  is  opened,  and  then  closes  them  gradually 
after  the  door  is  shut.  The  time  of  closing  is  usually  about  three 
minutes.  The  same  result  can  be  accomplished  by  the  fireman  regu- 
lating the  dampers  in  the  fire  door  by  hand.  In  some  cases  the  use 
of  a steam  jet  immediately  after  firing  has  proved  advantageous, 
since  it  not  only  carries  in  the  air  necessary  for  the  combustion  of  the 
volatile  gases,  but  also  serves  thoroughly  to  mix  the  air  and  gases. 

14.  Stoker  Firing. — It  is  not  within  the  scope  of  this  discus- 
sion to  give  detailed  instructions  for  the  use  of  different  types  of 
stokers.  All  the  statements,  however,  concerning  tight  settings, 
determination  of  proper  fuel  bed  thickness,  draft,  soot,  etc.,  apply  to 
stoker  firing  as  well  as  to  hand  firing.  Most  stokers  accomplish  one 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


43 


prime  requisite  for  good  combustion,  i.e.,  a uniform  supply  of  coal 
and  air,  but  they  require  as  intelligent  attention  as  does  hand  firing. 
Stokers  should  be  inspected  regularly  to  see  that  all  ledge  plates, 
baffles,  and  other  devices  designed  to  decrease  air  leakage  are  per- 
forming their  functions  properly.  The  grate  should  be  kept  uni- 
formly covered  with  fuel  and  the  rate  of  feed  adjusted  so  as  to  mini- 
mize the  amount  of  unburned  coal  carried  over  into  the  ashpit.  The 
chain  grate  stoker  is  probably  more  generally  used  for  Illinois  coal 
than  any  other  type,  and  it  has  usually  proved  satisfactory.  It  is 
used  largely  for  burning  slack,  or  screenings,  and  for  this  purpose 
a fuel  bed  of  about  six  inches  gives  the  best  results,  particularly 
when  natural  draft  is  used.  Detailed  instructions  for  the  operation 
of  any  particular  type  of  stoker  may  be  obtained  from  the  company 
building  it. 


44 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


IY.  Features  of  Boiler  Installation  in  Relation 
to  Fuel  Economy 

15.  Boiler  Bettings. — The  boiler  setting  consists  of  the  founda- 
tion and  such  parts  of  the  furnace  and  gas  passages  as  are  external 
to  the  boiler  shell.  The  setting  must  furnish  a proper  support  for  the 
boiler  and  at  the  same  time  provide  the  necessary  passages  for  the 
products  of  combustion  as  well  as  a pit  for  the  ashes. 

Foundation 

A good  solid  foundation  resting  on  a firm  footing  is  absolutely 
necessary  to  insure  a boiler  setting  which  will  remain  tight  and  free 
from  any  tendency  to  crack.  The  depth  of  the  foundation  and  the 
width  of  the  footings  necessary  for  a given  installation  depend  upon 
the  character  of  the  soil.  In  the  case  of  good  solid  soil  capable  of  sup- 
porting heavy  loads,  the  excavation  need  not  be  made  very  deep,  but 
where  the  ground  is  soft  it  is  well  to  excavate  the  entire  space  occupied 
by  the  setting  and  to  construct  a bed  of  concrete  about  two  feet  thick 
upon  which  the  walls  may  be  supported. 

When  boilers  are  supported  on  steel  columns,  as  is  usually  the 
case  with  water  tube  boilers  and  as  is  desirable  for  fire  tube  boilers 
also,  the  footings  at  the  base  of  the  columns  must  be  enlarged,  since 
with  such  means  of  support  the  loads  are  concentrated  and  not  dis- 
tributed as  in  the  case  of  horizontal  return  tubular  boilers  supported 
by  a series  of  lugs  resting  on  the  walls  of  the  setting.  In  general,  the 
foundation  for  all  types  of  boilers  should  be  very  rigid ; a weak  found- 
ation will  always  cause  the  setting  to  crack  no  matter  how  well  the 
brick  in  the  walls  may  be  set.  Weak  foundations  may,  furthermore, 
tend  to  produce  severe  stresses  at  pipe  connections  to  the  boiler  which 
are  likely  to  cause  trouble. 

Side  and  End  Walls 

The  side  and  rear  walls  are  supported  upon  the  foundation  and  in 
the  older  designs  of  settings  a two-inch  air  space  is  generally  provided 
in  these  walls.  In  many  of  the  newer  types  of  setting,  however,  this 
air  space  has  been  omitted.  As  a result  of  a series  of  experiments 
made  by  the  United  States  Geological  Survey,  it  has  been  found  that 
the  two-inch  air  space  provided  in  the  walls  of  boiler  settings  has 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


45 


practically  no  effect  in  preventing  the  flow  of  heat  from  the  interior 
of  the  setting.  As  a matter  of  fact  the  radiation  losses  for  a wall  with 
an  air  space  are  greater  than  those  for  a solid  wall.  In  order  to 
strengthen  the  side  walls,  buck-stays  held  together  by  long  bolts  are 
used.  The  furnace,  the  bridge  wall,  and  all  parts  of  the  side  and  rear 
walls  including  the  back  arch  which  are  exposed  to  the  hot  gases  must 
be  lined  with  high  grade  fire  brick  capable  of  withstanding  the  high 
temperatures.  The  fire  brick  should  be  backed  with  hard,  well  burned, 
red  bricks  laid  in  a high  grade  mortar.  All  arches,  piers,  and  wing 
walls  which  may  form  a part  of  the  combustion  chamber  should  be 
made  entirely  of  fire  brick. 

Settings  for  Horizontal  Return  Tubular  Boilers 
In  order  to  use  soft  coal  economically  it  is  desirable  to  obtain  as 
complete  combustion  as  possible.  Complete  combustion  also  means 
elimination  of  smoke.  To  obtain  proper  combustion  sufficient  air  must 
be  introduced  into  the  furnace  to  supply  the  necessary  oxygen.  The 
air  thus  introduced  must  mix  thoroughly  with  the  gases  given  off  by 
the  burning  coal  and  the  mixture  thus  obtained  must  be  kept  at  a high 
temperature  until  the  process  of  combustion  is  completed.  The  old 


Fig.  8.  Hartford  Setting  for  Return  Tubular  Boilers 

This  setting  does  not  satisfy  the  conditions  for  smokeless  combustion.  In  fact  it  is,  for 
Central  Western  coals,  very  unsatisfactory  and  should  not  be  used. 


The  setting  shown  in  the  above  figure  is  no 
longer  used  or  approved  by  the  Hartford  Steam 
Boiler  Inspection  and  Insurance  Co.  This  com- 
pany has  made  very  material  changes  in  the  de- 
sign of  their  horizontal  return  tubular  boiler  set- 
tings in  recent  years. 


m 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


Dimensions  of  Double -arch  Bridgewall  Jeff  mg  for  Horizontal 

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Fig.  9.  Double  Arch  Bridge  Wall  Setting  for  Smokeless  Combustion 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


47 


standard  setting1  for  return  tubular  boilers  (shown  in  Fig.  8)  is  fre- 
quently used,  but  it  does  not  satisfy  the  conditions  stated  and  for  this 
reason  should  not  be  used  when  smokeless  combustion  is  required.  In 
recent  years  several  types  of  settings  have  been  devised  which  if  pro- 
perly fired  make  possible  the  satisfactory  combustion  of  bituminous 
coal. 

A type  of  horizontal  return  tubular  boiler  setting  which  has  given 
good  results  with  soft  coals  is  shown  in  Fig.  9.  It  was  originated  and 
perfected  by  the  engineers  associated  with  the  Department  of  Smoke 
Inspection  of  the  City  of  Chicago  and  is  generally  recommended  for 
boilers  operating  at  a steam  pressure  of  sixty  pounds  or  more.  This 
setting  differs  from  that  illustrated  in  Fig.  8 in  that  a series  of  arches 
are  constructed  over  the  bridge  wall  and  in  the  combustion  chamber. 
A double-arch  rests  on  the  bridge  wall  and  on  a suitable  pier  built  up 
between  the  bridge  wall  and  a single  span  deflection  arch,  the  latter 
being  located  from  two  to  three  feet  back  of  the  bridge  wall.  The 
highest  point  of  this  deflection  arch  is  at  the  elevation  of  the  top  of 
the  bridge  wall  or  somewhat  below  it.  So  as  to  prevent  the  gases  from 
passing  over  the  arches  bulkheads  extending  up  to  the  boiler  are  con- 
structed above  them. 

It  is  evident  from  this  brief  description  that  the  gases  in  passing 
from  the  grate  over  the  bridge  wall  are  divided  into  two  separate 
streams  by  the  central  pier  supporting  the  double-arch.  In  going 
through  the  retorts  formed  by  the  double-arch  and  the  side  walls  of 
the  setting  the  gases  are  thoroughly  mixed  and  at  the  same  time  are 
subjected  to  high  temperatures.  Having  passed  through  the  retorts 
the  gases  are  compelled  to  change  their  direction  of  travel  so  as  to  pass 
under  the  deflection  arch  back  of  the  bridge  wall,  thus  promoting 
further  mixing  and  thereby  insuring  proper  combustion.  The  setting 
is  also  provided  with  the  usual  panel  door  for  the  admission  of  air  over 
the  fire.  The  steam  jets  shown  extending  through  the  furnace  front 
are  generally  considered  standard  equipment  and  it  is  recommended 
that  they  be  freely  used  after  each  firing. 

The  arches  used  in  connection  with  the  setting  shown  in  Fig.  9 
produce  a side  pressure  on  the  walls,  and  in  order  to  prevent  bulging 
and  cracking  of  the  walls  additional  buck-stays  and  tie  rods  should  be 
installed.  The  floor  of  the  combustion  chamber  is  subjected  to  high 
temperatures  and  for  this  reason  should  be  paved  with  second-grade 
fire  brick  laid  on  edge. 


48 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


According  to  Osborne  Monnett  * the  following  general  propor- 
tions should  be  satisfied  in  order  to  obtain  satisfactory  service  with 
this  type  of  setting. 

(1)  The  free  area  through  the  double-arch  above  the  bridge 
wall  should  be  made  equivalent  to  at  least  25  per  cent  of  the 
grate  area. 

(2)  The  area  from  the  back  of  the  bridge  wall  to  the  deflection 
arch  should  be  at  least  45  per  cent  of  the  grate  area. 

(3)  The  area  under  the  deflection  arch  should  be  at  least  50  per 
cent  of  the  grate  area. 

For  convenience  of  reference  the  dimensions  indicated  in  Fig.  9 
for  various  sizes  of  boilers  are  given  in  the  table  presented  with  the 
illustration.  These  dismensions  were  obtained  from  a report  submitted 
by  the  Standards  Committee  at  the  eleventh  annual  convention  of  the 
Smoke  Prevention  Association. 

There  are  several  patented  settings  in  which  the  gases  are  main- 
tained at  a high  temperature  and  are  thoroughly  mixed  by  the  use  of 
piers  and  wing  walls  in  place  of  the  arches  shown  in  the  setting  of 
Fig.  9.  Experience  seems  to  indicate  that  the  temperature  in  the  com- 
bustion chamber  of  such  settings  is  sufficiently  high  to  promote  proper 
combustion,  and  furthermore  it  is  claimed  that  they  burn  coal  with 
good  economy  and  are  cheaper  to  construct  than  the  double-arch 
setting. 

Settings  for  Water  Tube  Boilers 

A large  number  of  hand  fired  water  tube  boilers  of  the  horizontal 
type  designed  for  the  use  of  soft  coal  are  installed  with  what  is  gener- 
ally called  the  standard  vertical  baffling.  This  form  of  baffling  compels 
the  gases  to  pass  across  the  tubes,  thus  producing  a rather  short  flame 
travel  in  the  first  pass  and  rendering  complete  combustion  impossible. 
In  order  to  improve  combustion  in  hand  fired  water  tube  boilers  of 
the  horizontal  type  when  burning  soft  coal,  it  has  been  demonstrated 
by  the  Chicago  Department  of  Smoke  Inspection  that  the  setting 
should  be  so  arranged  as  to  fulfill  the  following  specifications:! 

* “Hand  Fired  Furnaces  for  Water  Tube  Boilers — I.”  Power,  Vol.  40,  p.  264,  August 
25,  1914. 
t Ibid. 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


49 


(1)  Some  provision  must  be  made  so  that  the  bottom  row  of 
tubes  will  absorb  some  heat  directly  from  the  fire.  This  is 
accomplished  by  the  use  of  T -tiles,  thus  exposing  the  bottom 
row  of  tubes  to  the  fire  for  a short  distance  from  the  front 
header. 

(2)  Over  the  bridge  wall  and  for  some  distance  back  of  it  a 
high  temperature  zone,  through  which  the  gases  and  air  pass, 
must  be  provided.  This  zone  is  obtained  by  using  box-tiles 
around  the  bottom  tubes.  The  box-tiles  extend  from  the  end  of 
the  T-tiles  to  a point  several  feet  in  front  of  the  back  header. 
The  area  provided  between  the  bridge  wall  and  the  box-tile 
should  be  made  equivalent  to  25  per  cent  of  the  grate  area. 

(3)  In  order  that  the  gases  and  air  will  thoroughly  mix,  a de- 
flecting arch  is  provided  a short  distance  back  of  the  bridge 
wall.  The  distance  between  the  arch  and  the  bridge  wall 
should  be  such  that  the  area  obtained  between  them  is  equiv- 
alent to  40  per  cent  of  the  grate  area.  The  height  of  the  arch 
must  be  sufficient  so  as  to  provide  an  area  underneath  it 
equivalent  to  50  per  cent  of  the  grate  area. 

(4)  As  in  the  case  of  the  horizontal  return  tubular  boiler  set- 
tings, excess  air  is  provided  through  the  panel  doors  in  addi- 
tion to  a siphon  steam  jet  located  above  the  fire  doors. 

When  water  tube  boilers  are  very  wide,  it  may  be  necessary  to 
construct  the  deflection  arch  mentioned  in  (3)  in  two  or  three  spans. 
These  spans  should  be  supported  on  suitable  piers  in  order  to  relieve 
the  strain  on  the  side  walls.  In  case  the  area  over  the  bridge  wall  is 
in  excess  of  25  per  cent  of  the  grate  area,  the  desired  area  may  be 
obtained  by  introducing  piers  upon  the  bridge  wall  opposite  the  spans 
in  the  deflection  arch.  Due  to  these  piers  the  gases  and  air  will  be 
more  thoroughly  mixed,  thus  promoting  combustion. 

In  water  tube  boilers  equipped  with  horizontal  baffles  it  generally 
happens  that  there  are  parts  of  certain  tubes  which  are  not  acted  upon 
effectively  by  the  gases.  This  is  due  to  the  fact  that  the  gases  become 
trapped  in  the  corners  as  shown  at  A in  Fig.  10  and  become  inert. 
Such  a condition  can  be  improved  with  a gain  in  the  efficiency  of  the 
boiler,  by  providing  openings  approximately  one  inch  wide  in  alter- 
nate rows  of  the  tile  B,  Fig.  10. 


50 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


One  of  the  most  serious  defects  found  in  brick  settings  is  air  leak- 
age. The  fire  brick  used  on  the  interior  of  the  setting  must  be  selected 
with  great  care  as  the  life  of  the  setting  very  largely  depends  upon  the 
quality  of  these  bricks  as  well  as  upon  the  workmanship  in  laying 
them.  Generally  the  arches  used  in  settings  cause  more  trouble  than 


Fig.  10.  Sketch  Showing  Effects  of  Baffling  and  Dampers  in  Causing 
Pockets  and  Eddies  in  the  Flue  Gas  Stream 


Defects  in  Settings 

any  other  part  of  the  setting.  In  some  cases  arches  fail  because  of 
the  use  of  a grade  of  brick  not  suited  to  the  purpose,  but  more  fre- 
quently failures  are  due  to  poor  workmanship  in  laying  the  bricks.  Air 
leakage  through  the  setting  can  be  reduced  by  pointing  up  the  brick 
work  in  the  proper  manner  and  by  covering  the  entire  setting  with  an 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


51 


insulating  material,  as  for  example  a high  grade  of  asbestos  or  magnesia 
covering.  The  exposed  parts  of  the  shell  of  horizontal  return  tubular 
boilers  and  of  the  steam  drums  of  water  tube  boilers  should  be  covered 
with  an  85  per  cent  magnesia  covering  two  or  three  inches  thick.  The 
outer  surfaces  of  all  insulating  materials  should  be  finished  off  with  a 
thin  coating  of  hard  cement  or  covered  with  canvas  and  painted.  If 
the  walls  of  the  setting  are  constructed  with  air  spaces  these  spaces 
should  be  filled  with  sand  or  ashes.  The  baffles  on  the  interior  of  the 
setting  should  be  kept  tight  so  that  the  gases  cannot  be  by-passed 
through  the  heating  surfaces.  All  steam  and  water  leaks  around  a 
boiler  should  be  stopped  immediately  since  water  coming  in  contact 
with  heated  brick  work  is  likely  to  cause  rapid  disintegration  of  the 
brick.  The  setting  should  be  so  constructed  that  the  boiler  is  free  to 
expand  without  affecting  the  brick  work. 


52 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


V.  Installation  Features  Affecting  Draft 
Conditions 

16.  Stacks  and  Breechings. — The  purpose  of  a stack  is,  of  course, 
to  supply  air  to  the  fuel  which  is  burning  on  the  grates  of  the  boiler 
furnace  and  then  to  remove  the  flue  gases  which  are  formed  after  they 
have  passed  over  the  boiler  surfaces  and  given  up  most  of  their  heat 
to  the  water  and  steam  in  the  boiler.  The  stack  may  waste  coal  if  the 
fireman  allows  it  to  supply  too  much  or  too  little  air,  or  if  he  allows 
the  flue  gases  to  leave  the  boiler  at  too  high  a temperature.  Most 
stacks  supply  too  much  air  so  that  a large  amount  of  heat  is  carried 
away  in  the  unnecessarily  large  volume  of  flue  gases  formed  when  this 
air  passes  through  the  fuel  bed,  where  it  not  only  serves  to  burn  the 
coal  but  also  takes  up  heat. 


Fig.  11.  An  Approved  Form  of  Hinged  Damper 
The  Stack  Damper  and  Its  Use 

In  order  to  control  the  amount  of  air  and  flue  gas  passing  to  a 
stack,  a damper  (Figs.  10  and  11)  should  be  installed  at  the  point 
where  the  flue  gas  leaves  each  boiler.  This  damper  should  fit  tight 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


53 


and  true  and  should  move  easily.  An  approved  form  of  damper,  which 
is  tight  fitting,  is  shown  in  Fig.  11.  It  should  have  a free  opening 
about  25  per  cent  greater  than  the  area  through  the  tubes.  Long 
narrow  dampers  are  to  be  avoided  wherever  possible.  For  water  tube 
boilers  the  damper  opening  should  be  about  0.25  of  the  grate  area. 
The  damper  must  be  opened  only  enough  to  permit  the  stack  to  supply 
the  right  amount  of  air  to  burn  completely  the  fuel  fired.  When  the 
demand  for  steam  increases,  more  coal  must  be  burned  and  the  damper 
must  be  opened  wider  in  order  to  supply  more  air.  The  air  supply 
should  not  be  controlled  by  opening  and  closing  the  ashpit  doors, 
which  should  stand  wide  open  practically  all  the  time.  If  the  stack  is 
not  controlled  by  the  damper,  it  will  always  exert  its  full  power  on  the 
setting  which  means  that  the  tendency  for  air  to  leak  in  at  any  cracks 
and  joints  will  be  as  great  at  half  load  as  at  full  load,  and  even  with 
the  ashpit  doors  closed  this  leakage  would  be  unchanged  if  the  stack 
damper  remained  open. 

From  what  has  been  stated,  it  is  evident  that  a stack  must  be  cap- 
able (at  full  damper  opening)  of  supplying  all  the  air  that  the  boiler 
may  require  when  burning  coal  at  the  highest  rate  (pounds  per  hour) 
necessary  for  the  maximum  load.  At  all  other  rates  of  burning  coal 
the  damper  must  be  partly  closed,  and  in  many  plants,  since  the  stack 
is  too  powerful  (supplies  too  much  air)  even  for  the  highest  rate  of 
burning  coal,  the  damper  must  never  be  fully  opened;  otherwise  too 
much  air  will  pass  through  the  grates  and  fuel  will  be  wasted. 

In  order  that  the  approximate  capacity  of  a stack  may  be  checked 
against  the  load  it  should  carry,  Table  3 has  been  arranged  in  con- 
venient form  for  ready  reference.  Thus,  if  a certain  boiler  plant  is 
burning  2,800  pounds  of  coal  an  hour  at  its  maximum  capacity  and  the 
stack  is  100  feet  high,  the  diameter  should  be  60  inches, 

Table  3 is  a modification  of  William  Kent’s  stack  table  and  is  re- 
liable for  the  ordinary  rates  of  combustion  with  bituminous  coals. 
The  values  in  the  table  give  the  pounds  of  coal  burned  per  hour.  With 
coal  of  fair  grade  it  is  necessary  to  burn  about  five  pounds  per  boiler 
horse-power,  but  with  low  grade  bituminous  coal  it  is  necessary  to 
burn  from  six  to  eight  pounds  per  boiler  horse-power.  . For  example, 
in  the  boiler  plant  already  considered,  burning  2,800  pounds  of  coal  an 
hour,  a stack  100  feet  high  and  60  inches  in  diameter  would  provide 
only  for  400  boiler  horse-power,  if  a poor  grade  of  middle  western  coal 
was  used  requiring  seven  pounds  per  boiler  horse-power. 


54 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


Table  3 

Stack  Sizes  Based  on  Kent’s  Formula 


Diameter 

Inches 

Area 

Square  Feet 

Height 

OF  STACK  IN  FEET 

Side  of  Equivalent 

Square  Stack,  In. 

Diameter 

1 Inches 

50 

60 

70 

80 

90 

100 

110 

125 

150 

175 

Pounds  of  Coal  Burned  per  Hour 

33 

5.94 

530 

575 

625 

665 

705 

745 

30 

33 

36 

7.07 

645 

705 

760 

815 

865 

910 

32 

36 

39 

8.30 

775 

845 

915 

980 

1040 

1095 

1145 

1225 

35 

39 

42  _ 

9.62 

915 

1000 

1080 

1155 

1225 

1290 

1355 

1445 

1580 

38 

42 

48 

12.57 

1230 

1345 

1450 

1555 

1650 

1740 

1825 

1945 

2130 

2300 

43 

48 

54 

15.90 

1590 

1740 

1880 

2010 

2135 

2245 

2360 

2515 

2755 

2975 

48 

54 

60 

19.64 

2000 

2185 

2365 

2525 

2680 

2825 

2965 

3160 

3460 

3740 

54 

60 

66 

23.76 

2450 

2685 

2900 

3100 

3290 

3470 

3640 

3800 

4245 

4590 

59 

66 

72 

28.27 

2955 

3230 

3490 

3735 

3960 

4175 

4380 

4670 

5115 

5525 

64 

72 

78 

33.18 

3500 

3830 

4140 

4425 

4695 

4950 

5190 

5535 

6060 

6550 

70 

78 

84 

38.48 

4090 

4480 

4840 

5175 

5490 

5785 

6070 

6470 

7090 

7655 

75 

84 

Height 

of  Stack  in 

Feet 

100 

110 

125 

150 

175 

200 

225 

250 

Pounds  of 

Coal  Burned 

per  Hour 

90 

44.18 

6690 

7015 

7480 

8195 

8850 

9465 

10040 

10580 

80 

90 

96 

50.27 

7660 

8080 

8565 

9380 

10135 

10835 

11490 

12115 

86 

96 

102 

56.75 

8695 

9120 

9720 

10650 

11500 

12295 

13045 

13750 

91 

102 

108 

63.62 

9795 

10270 

10950 

11960 

12960 

13850 

14695 

15490 

98 

108 

114 

70.88 

10960 

11495 

12255 

13425 

14500 

15500 

16440 

17330 

101 

114 

120 

78.54 

12190 

12785 

13630 

14930 

16130 

17240 

18285 

19275 

107 

120 

126 

86.59  • 

13485 

14145 

15080 

16515 

17840 

19070 

20230 

21325 

112 

126 

132 

95.03 

14850 

15570 

16605 

18185 

19645 

21000 

22275 

23480 

117. 

132 

144 

113.10 

17770 

18630 

19865 

21760 

23505 

25130 

26655 

28090 

128 

144 

156 

132.73 

20950 

21965 

23420 

25655 

27710 

29625 

31425 

33120 

138 

156 

168 

153.94 

24390 

25 

575 

27270 

29870 

32270 

34495 

36590 

38565 

150 

168 

“Draft”  is  in  Reality  a Pressure 

It  must  be  remembered  that  air  enters  the  ashpit,  or  rushes 
through  the  open  fire  door,  or  through  any  cracks  or  crevices  in  the 
setting  or  breeching  because  the  surrounding  outside  air  is  always 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


55 


heavier  than  the  hot  flue  gas  in  the  stack  and  setting,  and  hence  exerts 
an  inward  pressure  at  all  points.  The  so-called  “ draft”  over  the 
grate  as  shown  by  a draft  gage  (Figs.  3 and  4)  is  an  indication  of  this 
difference  in  pressure  or  tendency  for  the  outside  air  to  crowd  its  way 
into  the  furnace  and  boiler  setting.  In  order  to  understand  why  this 
tendency  exists  and  why  draft  is  a true  pressure  and  not  a suction 


\ 


M 

v; 


Fig.  12.  Isometric  Sketch  Illustrating  the  Principle  that  Light  Fluids  or 
Gases  are  Pushed  Upward  when  in  Contact  with  Heavier  Fluids  or  Gases 

In  this  case  the  lighter  fluid,  oil  (shown  in  red),  is  pushed  up  by  the  heavier  fluid,  water 
(shown  in  green).  The  force  pushing  the  oil  up  the  tube  is  0.086  pounds  per  square  inch. 


refer  to  Fig.  12.  It  will  be  evident  that,  since  the  column  of  water 
two  feet  high  weighs  more  per  square  inch  than  a similar  column  of 
oil,  the  water  will  push  the  oil  up  the  tube  in  the  same  way  that  the 


56 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


cold  outside  air  pushes  through  the  grates  of  a boiler  furnace  and 
forces  the  hot  flue  gas  up  the  chimney.  If  there  is  a fire  burning  on 
the  grate  the  action  is  continuous,  and  outside  air  will  continue  to 


Note:  The  inward  air 
pressure  aga/nst  ttr* 
setting  at  th/s  po/nt 
is  egu/va/ent  to  the 
cotumn(c)  on  gage  board. 
See  gage  No  e 


Gaqe  doard 

Draft  gages  read  m inches 


Water  column  a 
b 
c 
d 
e 
f 

g 


= Total  draft  avai/ab/e  at  damper 

- Loss  of  draft  through  boiler  tubes. 

- Draft  available  at  rear  arch 
= Loss  of  draft  between  furnace  and  ' 

- Draft  over  fire  in  furnace. 

- Loss  of  draft  through  grates  and  fuet  bed 

- Loss  of  draft  through  ash  pit  door  opening. 


Fig.  13.  Sketch  Showing  Variations  in  Draft  at  Different  Points  and 
Indicating  Tendency  Toward  Air  Leakage 


enter  the  ashpit  (Fig.  13)  and  push  its  way  through  the  bed  of  fuel 
on  the  grate,  thus  promoting  the  combustion  of  the  fuel. 

Air  Leaks  Affect  the  Draft  and  Waste  Coal 
If  cold  air  leaks  into  the  setting  at  any  point,  it  will  result  in  two 
forms  of  fuel  waste.  First,  it  will  cool  the  gases  in  the  setting  and  in 
the  chimney  and  will  make  the  draft  less.  This  may  make  it  difficult 
to  burn  the  fuel  properly.  Secondly,  the  air  which  has  leaked  in  must 
be  warmed  up,  thus  taking  heat  away  from  the  boiler  and  wasting  it 
through  the  chimney,  and  finally  this  air  will  so  increase  the  volume 
of  flue  gas  that  it  may  be  difficult  for  the  chimney  to  handle  the  in- 
creased volume  of  flue  gas  even  with  the  damper  wide  open. 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


57 


Breechings  for  a Battery  of  Two  or  More  Boilers 

Many  breechings  serving  more  than  one  boiler  are  condemned  as 
being  too  small  because  so  much  unnecessary  air  is  leaking  into  the 
various  settings  that  the  breeching  cannot  handle  both  the  leakage 
and  the  necessary  flue  gas.  By  systematically  stopping  all  the  leaks 
such  a breeching  will  often  easily  handle  the  flue  gases  resulting  from 
the  minimum  air  supply  actually  required  for  burning  the  fuel. 
Breechings  should  be  at  least  from  10  to  15  per  cent  greater  in  area 
than  the  stack  to  which  they  connect. 

The  individual  boiler  dampers  in  the  throat  or  uptake  connections 
opening  into  a breeching  should  fit  accurately  and  close  tightly,  other- 
wise it  will  be  impossible  to  prevent  cold  air  from  entering  the  main 
breeching  through  the  damper  of  a “dead”  boiler.  This  will  often 
seriously  affect  the  operation  of  all  the  other  boilers  by  “checking” 
the  draft  of  the  stack  which  serves  the  boilers  connected  to  this  breech- 
ing. 

Breechings  should  be  as  short  and  straight  as  possible,  and  should 
have  no  sharp  angles  around  which  the  flue  gases  may  swirl  and  eddy 
in  their  passage  to  the  stack.  The  bad  effect  of  sharp  angles  is  shown 
in  the  stack  connection  marked  “B”  in  Fig.  14.  The  method  of  cor- 
recting this  difficulty  is  shown  at  “A”  in  the  same  figure.  Breech- 
ings should  be  covered  with  a good  heat  insulating  material  or  lined 
with  a refractory  brick  or  vitrified  material. 

All  boiler  dampers  should  be  “calibrated,”  that  is,  should  have 
the  operating  lever  or  chain  so  marked  and  set  that  the  draft  for  boiler 
No.  1,  nearest  the  stack  (Fig.  14),  will  be  no  greater  than  for  boiler 
No.  3,  farthest  from  the  stack,  when  both  boilers  are  clean  and  have 
the  same  thickness  of  fuel  bed.  To  accomplish  this  result  it  may  be 
found  that  the  damper  on  the  nearest  boiler  must  be  nearly  closed  most 
of  the  time.  If  all  dampers  are  set  at  the  same  angle  without  regard 
to  their  location  with  reference  to  the  stack,  too  much  air  will  go 
through  the  nearest  boiler  or  the  farthest  boiler  will  get  too  little  air 
and  suffer  a loss  in  capacity. 

Conditions  Under  Which  a Stack  Will  Operate  Economically 

If  fuel  is  to  be  used  economically,  the  stack  must  supply  the  fur- 
nace with  just  enough  air  to  burn  the  fuel  completely.  This  can  only 
be  done  when  the  following  conditions  are  observed : 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


59 


(1)  The  setting  must  be  made  air  tight.* 

(2)  All  doors  and  door  frames  opening  into  setting  and  breech- 
ing must  be  made  to  fit  air  tight. 

(3)  The  breeching  and  stack  should  likewise  be  made  air  tight 
and  should  be  well  insulated  to  prevent  heat  loss  from  the 
flue  gases  so  that  all  the  heat  in  the  gases  may  be  available 
for  creating  draft. 

(4)  The  air  used  for  burning  the  fuel  should  all  enter  through 
the  ashpit,  except  a limited  and  carefully  regulated  air  supply 
which  should  be  admitted  through  the  fire  door  after  firing 
fresh  coal. 

(5)  When  natural  draft  is  employed,  the  control  of  the  air 
should  be  accomplished  by  operating  the  stack  or  breeching 
damper  according  to  the  rate  of  burning  coal  and  never  by 
opening  and  closing  the  ashpit  doors. 


* A candle  flame  is  commonly  used  to  detect  air  leaks  into  a setting  since  it  will  be 
drawn  into  any  crevice  through  which  air  is  entering. 


GO 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


VI.  Feed  Water  Heating  and  Purification  as  Factors 
in  Fuel  Economy 

17.  Feed  Water  Purification. — The  majority  of  waters  used  for 
boiler  feeding  purposes  contain  more  or  less  impurities  which  are 
deposited  in  the  boiler.  Such  deposits  of  foreign  matter  tend  to  de- 
crease the  evaporative  capacity  of  the  boiler  and,  if  they  are  not  re- 
moved, will  frequently  cause  overheating  of  tubes  and  sheets.  To 
overcome  these  difficulties  the  impurities  in  the  feed  water  should  be 
removed  before  feeding  into  the  boiler. 

For  convenience  of  reference,  the  impurities  most  often  found 
in  feed  water  and  their  effects  upon  the  sheets  and  tubes  if  permitted 


Table  4 

Impurities  in  Feed  Waters,  their  Effects  and  Remedies* 


Impurities 

Effects 

Remedies 

1 

2 

3 

Sediment,  mud,  clay,  etc. 
Bicarbonates  of  lime,  magnesia 
Sulphates  of  lime  and  magnesia 

Incrustation  and  the  for- 
mation of  sludge 

Settling  tanks,  filtration,  blowing 
down. 

Blow  down. 

Heat  feed  water.  Treat  by  adding 
lime. 

Treat  by  adding  soda.  Barium 
carbonate. 

Chloride  and  sulphate  of  magnesia 
Acid 

Dissolved  carbonic  acid  and  oyx- 
gen 

Grease 

Organic  matter 

Corrosion 

Treat  by  adding  carbonate  of  soda. 

Soda  or  lime. 

Heat  feed  water.  Keep  air  from 
feed  water.  Add  caustic  soda 
or  slacked  lime. 

Filter.  Iron  alum  as  coagulant. 
Neutralize  with  carbonate  of 
soda.  Use  the  best  of  hydro- 
carbon oils. 

Filter.  Use  coagulant. 

Sewage 

Readily  soluble  salts  in  large 
quantities 

Carbonate  of  soda  in  large 
quantities  2 

Priming 

Settling  tanks.  Filter  in  con- 
nection with  coagulant. 

Blow  down. 

Barium  carbonate.  New  feed 
supply.  If  from  over  treat- 
ment, change  or  modify. 

Steam,”  published  by  Babcock  & Wilcox  Company. 

2 May  cause  brittleness  in  plates.  See  Bulletin  94,  Eng.  Exp.  Sta.  Univ.  of  111.,  “The  Embrittling 
Action  of  Sodium  Hydroxide  on  Soft  Steel,”  by  S.  W.  Parr. 


to  enter  the  boiler  are  given  in  columns  1 and  2 of  Table  4.  In  the 
last  column  of  this  table  are  given  the  usual  remedies  employed  to 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


61 


neutralize  or  to  prevent  to  a certain  degree  the  effects  produced  by  the 
various  impurities.  Some  of  the  impurities  found  in  feed  water  cause 
the  formation  of  scale  on  the  sheets  and  tubes,  others  cause  corrosion 
of  the  metal,  and  still  others  produce  priming,  or  the  carrying  over  of 
particles  of  water  with  the  steam  as  the  latter  leaves  the  boiler. 

18.  Treatment  of  Feed  Waters. — One  of  the  best  ways  of  deter- 
mining the  remedy  to  be  applied  in  overcoming  the  injurious  effects 
of  the  impurities  contained  in  the  feed  water  is  to  submit  a sample  of 
the  water  to  a reliable  chemist  for  analysis  and  prescription.  After 
such  an  analysis  has  been  made  it  is  possible  to  ascertain  which  one  of 
the  following  treatments  should  be  applied,  chemical  treatment,  heat 
treatment,  or  combined  heat  and  chemical  treatment. 

Chemical  Treatment 

The  chemical  treatment  of  feed  water  involves  the  use  of  either 
the  lime  or  the  soda  process  or  a combination  of  these  two.  The  first 
of  these  processes  in  which  slacked  lime  is  used  is  well  adapted  for 
precipitating  the  bicarbonate  of  lime  and  magnesia  contained  in  the 
feed  water.  In  the  soda  process  carbonate  of  soda  or  caustic  soda , 
either  separately  or  together,  is  used  for  converting  the  sulphates  of 
lime  and  magnesia  into  carbonates  or  chlorides  which  may  be  disposed 
of  by  occasional  blowing  off.  The  combination  of  the  lime  and  soda 
processes,  however,  is  most  frequently  used.  It  is  satisfactory  for 
treating  water  containing  sulphates  of  lime  and  magnesia,  carbonic 
acid,  or  bicarbonates  of  lime  and  magnesia.  In  this  process  the  sul- 
phates are  broken  down  by  the  use  of  sufficient  soda,  and  the  necessary 
lime  is  added  to  absorb  the  carbonic  acid  not  taken  up  in  the  soda  re- 
action. 

Heat  Treatment 

The  bicarbonates  of  lime  and  magnesia  so  often  found  in  natural 
waters  may  be  partially  precipitated  by  preheating  the  feed  water  in 
some  form  of  apparatus  commonly  called  a heater.  The  sulphates  of 
lime  and  magnesia,  however,  require  high  temperatures  for  complete 
precipitation  and  it  is  impossible  to  remove  these  impurities  by  the 
simple  process  of  preheating  in  the  ordinary  heater  using  exhaust 
steam.  Instead,  live  steam  heaters  and  economizers  are  required  for 
removing  them. 


62 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


Combined  Chemical  and  Heat  Treatment 

Since  preheating  of  feed  water  removes  the  carbonates  of  lime 
and  magnesia,  many  water  purification  systems  combine  the  chemical 
and  heat  treatments  discussed  in  the  preceding  paragraphs,  the  chem- 
ical treatment  being  used  merely  for  reducing  the  sulphates. 

19.  Boiler  Compounds. — So-called  boiler  compounds  are  used 
rather  extensively  for  treating  feed  water  and  no  doubt  in  many  cases 
the  results  obtained  are  satisfactory.  According  to  reliable  authori- 
ties the  use  of  compounds  is  recommended  for  the  prevention  of  new 
scale  rather  than  for  the  removal  of  old  scale.  In  general,  no  com- 
pound should  be  used  until  the  proper  advice  has  been  obtained  to  in- 
sure the  selection  of  the  right  compound  for  the  particular  feed  water 
to  be  treated.  In  no  event  should  the  use  of  boiler  compounds  be  re- 
garded as  a suitable  substitute  for  regular  cleaning  and  inspection. 

20.  Feed  Water  Heaters. — In  any  power  plant  of  considerable 
size  cold  water  should  not  be  fed  into  the  boilers,  since  all  steam  boilers 
are  more  or  less  seriously  affected  by  the  resulting  unequal  expansion 
and  contraction.  If  cold  water  is  forced  into  the  boiler,  the  tubes  of 
water  tube  boilers  are  very  likely  to  become  troublesome  while  in  re- 
turn tubular  boilers  the  seams  are  liable  to  develop  leaks.  Further- 
more the  feed  water  cannot  be  converted  into  steam  until  its  temper- 
ature is  raised  to  the  point  controlled  by  the  steam  pressure,  and  to  do 
that  requires  fuel.  If  the  temperature  of  the  feed  water  can  be  raised 
by  means  of  heat  which  otherwise  would  be  wasted,  it  is  good  economy 
to  do  so.  The  preheating  of  feed  water  also  increases  the  steaming  ca- 
pacity of  the  boiler,  because  of  the  reduction  in  the  amount  of  heat  to 
be  supplied  by  the  boiler  per  pound  of  water  evaporated.  With-certain 
types  of  feed  water  heaters  a considerable  portion  of  the  scale  forming 
ingredients  are  precipitated  before  the  water  enters  the  boiler,  thus 
increasing  the  efficiency  and  capacity  of  the  boiler  as  well  as  effecting 
a saving  in  the  expense  of  cleaning  out  the  boiler.  In  general,  it  may 
be  stated  that  one  per  cent  of  fuel  is  saved  for  every  eleven  degrees 
rise  in  the  feed  water  temperature,  provided  the  heat  producing  this 
rise  in  temperature  would  otherwise  be  wasted. 

In  steam  power  plants  there  are  two  main  sources  of  waste  heat, 
the  first  being  the  exhaust  steam  of  the  various  units,  and  the  second 
the  products  of  combustion  which  pass  from  the  boiler  to  the  chimney. 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


63 


The  heat  contained  in  the  drips  from  the  high  pressure  piping  system 
is  also  a source  of  loss  in  many  small  plants,  although  its  extent  is  not 
great.  Condensation  in  the  high  pressure  system,  which  includes  all 
piping  under  pressure  practically  equivalent  to  boiler  pressure,  is 
free  from  oil  and  should  be  returned  to  the  feed  water  heater  by  means 
of  pumps  or  traps.  If  desired  the  condensed  steam  may  be  returned 
directly  to  the  boiler.  In  steam  power  plants,  high  pressure  steam 
traps  are  generally  used  for  automatically  draining  the  condensation 
from  the  high  pressure  lines. 

Exhaust  Steam  Heaters 

Heaters  using  exhaust  steam  for  heating  the  water  may  be  either 
of  the  open  or  closed  type. 

An  open  heater  is  one  in  which  the  exhaust  steam  and  water 
mingle,  the  steam  in  condensing  giving  up  its  heat  directly  to  the 
water.  In  general  an  open  heater  consists  of  a shell  the  upper  part  of 
which  contains  a number  of  removable  trays.  The  function  of  these 
trays  is  to  break  up  the  incoming  feed  water  into  thin  streams  or 
layers.  In  passing  over  the  trays,  the  water  mingles  with  the  exhaust 
steam,  and  if  sufficient  steam  is  supplied  temperatures  as  high  as  210 
degrees  F.  may  result.  It  is  evident  that  in  an  open  heater  only  those 
scale  forming  ingredients  which  will  precipitate  below  210  degrees 
F.  will  be  deposited  in  the  heater.  Below  the  trays,  the  heater  is 
provided  with  a bed  of  coke  or  charcoal  through  which  the  water  is 
filtered  before  the  feed  pump  sends  it  into  the  boiler.  The  function 
of  the  coke  or  charcoal  filter  is  to  remove  the  precipitates  and  other 
suspended  impurities  coming  into  the  heater.  Open  heaters  should 
always  be  supplied  with  a suitable  oil  separator  for  removing  any  oil 
contained  in  the  exhaust  steam. 

Closed  Heaters 

In  a closed  heater  the  exhaust  steam  and  feed  water  do  not  come 
into  actual  contact  with  each  other,  the  steam  giving  up  its  heat  to  the 
water  by  conduction.  In  one  type  of  closed  heater  the  exhaust  steam 
surrounds  tubes  through  which  the  water  passes.  In  a second  type, 
the  steam  passes  through  tubes  which  are  surrounded  by  the  water. 
Closed  heaters  are  recommended  only  for  installations  where  the  feed 
water  is  free  from  scale  forming  ingredients,  since  there  is  a tendency 
for  the  tube  in  these  heaters  to  become  coated  with  a deposit  of  scale, 
thus  materially  decreasing  the  efficiency  of  the  apparatus. 


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ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


Advantages  and  Disadvantages  of  Exhaust  Steam  Heaters 

The  advantages  of  an  open  heater  are  as  follows : 

(1)  The  feed  water  may  reach  approximately  the  temperature  of 
the  exhaust  steam  provided  sufficient  steam  is  supplied. 

(2)  Scale  and  oil  do  not  effect  the  transmission  of  heat. 

(3)  The  pressure  in  an  open  heater  is  low,  practically  atmos- 
pheric. 

(4)  Scale  and  other  impurities  precipitated  in  the  heater  may 
easily  be  removed. 

(5)  An  open  heater  is  well  adapted  to  heating  systems  in  which 
it  is  desired  to  pipe  the  returns  direct  to  the  heater. 

(6)  The  initial  cost  of  an  open  heater  is  generally  less  than  that 
of  a closed  heater. 

(7)  With  the  open  heater  all  the  condensed  steam  is  returned  to 
the  system. 

The  disadvantages  of  an  open  heater  are  as  follows : 

(1)  Some  provision  must  be  made  for  removing  oil  from  the  ex- 
haust steam.  In  modern  open  heaters  this  is  accomplished 
by  effective  oil  separators  attached  directly  to  and  forming 
a part  of  the  heater. 

(2)  “ Sticking”  or  clogging  of  the  back  pressure  valve  may  sub- 
ject the  open  heater  to  excessive  pressure. 

(3)  If  the  feed  water  supply  is  under  suction,  open  heaters  may 
require  the  use  of  two  pumps,  one  for  hot  and  one  for  cold 
water. 

The  advantages  of  a closed  heater  are  as  follows : 

(1)  The  closed  heater  will  safely  withstand  any  ordinary  boiler 
pressure. 

(2)  Oil  does  not  come  in  contact  with  the  feed  water. 

(3)  It  is  the  only  type  of  heater  which  may  be  used  in  the  ex- 
haust main  between  a prime  mover  and  its  condenser. 

(4)  Since  it  is  customary  to  locate  a closed  heater  on  the  pressure 
side  of  the  feed  pump,  only  one  pump,  and  that  for  cold 
water,  is  necessary. 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


65 


The  disadvantages  of  a closed  heater  are  as  follows : 

(1)  Scale  and  oil  deposits  on  the  tubes  lower  the  heat  trans- 
mission. 

(2)  The  temperature  of  the  feed  water  will  always  be  from  four 
to  eight  degrees  below  the  temperature  of  the  incoming  ex- 
haust steam. 

(3)  Scale  in  the  tubes  is  removed  with  difficulty. 

21.  Economizers. — An  economizer  is  an  arrangement  of  vertical 
water  tubes  arranged  in  nests,  located  in  the  flue  between  the  boiler 
and  the  stack.  Its  purpose  is  to  heat  the  feed  water.  The  adjacent 
nests  of  tubes  are  connected  together  by  means  of  expansion  bends. 
To  prevent  deposits  of  soot,  the  tubes  are  provided  with  automatic 
scrapers  which  are  kept  moving  up  and  down  by  means  of  a suitable 
mechanism  driven  by  a motor  or  a small  steam  engine.  Since  the 
temperature  of  the  flue  gases  is  generally  about  550  degrees  F.,  it  is 
evident  that  considerable  heat  escapes  through  the  chimney.  In  gen- 
eral, the  load  factor,  the  size  of  the  plant,  and  the  cost  of  fuel  are 
factors  which  should  be  considered  in  determining  the  advisability  of 
installing  an  economizer. 

22.  Live  Steam  Heaters. — Live  steam  heaters  use  steam  at  boiler 
pressure  and,  as  mentioned  in  a preceding  paragraph,  are  primarily 
intended  for  purifying  the  feed  water.  Such  heaters  are  generally  not 
installed  unless  scale  forming  impurities  are  found  in  the  water.  At 
temperatures  less  than  300  degrees  F.  the  sulphates  of  lime  and  mag- 
nesia do  not  entirely  precipitate;  hence  a feed  water  containing  these 
impurities  will  not  be  thoroughly  purified  by  preheating  with  exhaust 
steam  at  atmospheric  pressure.  Reports  of  tests  tend  to  show  that  live 
steam  heaters  do  not  increase  boiler  efficiency,  but  merely  act  as  puri- 
fiers. Live  steam  heaters  should  always  be  by-passed  and  so  located 
that  the  bottom  of  the  shell  is  at  least  two  feet  above  the  water  level 
in  the  boiler,  thus  permitting  the  purified  water  to  gravitate  into  the 
boiler. 

23.  Feeding  Boilers. — Water  is  fed  to  the  boiler  by  means  of  an 
injector  or  a pump  depending  upon  the  size  of  the  plant.  The  use  of 
an  injector  does  not  permit  preheating  the  feed  water  by  means  of 
an  open  heater;  hence  relatively  cold  water  is  introduced  into  the 
boiler,  thus  decreasing  the  economy  of  the  plant.  It  is  possible  to 


66 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


install  between  the  injector  and  the  boiler  a closed  heater,  but  in  such 
an  installation  the  effectiveness  of  the  heater  is  decreased  because  of 
the  heat  supplied  by  the  injector.  Frequently  it  is  claimed  that  an 
injector  considered  as  a combined  pump  and  heater  has  an  efficiency 
of  one  hundred  per  cent  since  all  the  heat  in  the  steam  used  for  operat- 
ing the  injector  is  returned  with  the  water  forced  into  the  boiler.  Con- 
sidered as  a pump  the  injector  is  very  inefficient  since  it  requires  much 
more  steam  to  force  a given  amount  of  water  into  the  boiler  than  is  re- 
quired by  a pump  to  do  the  same  amount  of  work.  Furthermore  when 
a pump  is  used  for  feeding  boilers,  the  exhaust  steam  from  the  pump 
may  be  used  for  preheating  the  feed  water.  According  to  tests,  a 
direct  acting  steam  pump,  feeding  water  through  a heater  in  which 
the  exhaust  steam  of  the  feed  pump  is  utilized,  shows  a much  greater 
saving  of  fuel  than  an  ejector  with  or  without  a heater.  In  general 
the  feed  pump  must  be  located  below  the  water  level  in  the  heater, 
preferably  about  three  feet  below,  since  hot  water  cannot  be  lifted 
by  suction. 

In  order  that  it  may  be  possible  to  check  the  efficiency  of  the 
boiler  as  well  as  that  of  the  fireman  or  to  determine  the  most 
economical  fuel,  the  feed  water  system  should  include  some  form  of 
metering  device  for  measuring  the  water  fed  to  the  boilers.  There 
are  a number  of  metering  devices  on  the  market  some  of  which  are 
permanently  accurate  and  some  of  which  must  be  checked  up  at  fre- 
quent intervals.  There  are  now  several  manufacturers  of  feed  water 
heaters  who  are  prepared  to  furnish  heaters  equipped  with  water 
measuring  devices. 

In  addition  to  measuring  the  amount  of  water  fed  to  a boiler, 
provision  should  be  made  for  weighing  the  coal  used  by  each  boiler, 
thus  affording  a means  of  determining  for  each  boiler  the  evapora- 
tion per  pound  of  fuel.  This  will  also  make  it  possible  to  compare 
the  performance  of  any  two  boilers  in  the  plant. 

For  the  majority  of  small  boiler  plants  the  feed  water  should 
be  introduced  into  the  boiler  at  a constant  rate  rather  than  intermit- 
tently as  is  too  frequently  done. 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


67 


VII.  Steam  Piping  Requirements  for  Fuel  Economy 
in  Small  Plants 

24.  Possibility  of  Fuel  Loss  in  the  Transmission  of  Steam. — In 
order  to  promote  the  economical  use  of  coal,  the  steam  generated 
should  be  transmitted  to  the  point  of  use  with  as  little  loss  of  both 
heat  and  steam  as  practicable.  This  means  that  the  piping  system 
should  be  as  simple  as  possible  and  well  insulated.  Only  short  direct 
runs  should  be  used  in  connecting  boilers,  engines,  and  other  appa- 
ratus. 

All  branch  lines  not  in  use  should  have  the  valves  closed  so  that 
steam  cannot  enter  them  and  wrnste  heat  by  condensing  in  these  dead 
ends,  and  the  stop  valves  should  be  located  (Fig.  15)  so  as  to  accom- 
plish this  purpose.  If  the  engine  shown  in  Fig.  15  is  shut  down  for 
any  length  of  time  tlie  valves  at  both  ends  of  the  engine  lead  should 
be  closed  to  prevent  steam  from  condensing  in  and  filling  up  this 
lead. 


25.  Value  of  High  Pressure  Drips  as  Hot  Feed  Water. — Each 
high  pressure  header  and  steam  separator  should  be  dripped  (Fig.  15) 
and  the  hot  water  returned  to  the  feed-water  heater,  which  should 
be  included  in  the  equipment  of  every  power  plant  since  each  11 
degrees  F.  increase  in  the  feed-water  temperature  will  effect  a sav- 
ing of  nearly  one  per  cent  in  the  coal  burned.  In  no  case  should  cold 
water  be  fed  direct  to  the  boilers,  even  if  live  steam  has  to  be  used 
for  heating  it. 

The  oily  drips  from  the  exhaust  steam  header  (Fig.  15)  should 
be  discharged  to  the  sewer  or  wasted  since  the  oil  they  carry  has  an 
injurious  effect  upon  the  boiler  tubes  and  shell,  and  may  do  much 
more  harm  than  the  fuel  value  of  the  heat  contained  in  these  drips 
is  worth. 

26.  Leakage  Losses  at  Valves  and  Fittings. — The  boiler  blow-off 
cock  or  valve  must  be  perfectly  tight  to  prevent  the  escape  of  any 
hot  water  to  the  sewer  or  other  waste  channel.  If  the  end  of  this 
line  cannot  be  readily  inspected  to  make  sure  that  all  blow-off  valves 
are  tight,  then  a tell-tale  connection  (Fig.  15)  with  valve  should  be 


68 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


placed  in  the  blow-off  line  beyond  the  main  cock  so  that  by  opening 
it  a leak  at  the  blow-off  will  at  once  be  apparent. 

Leaks  of  hot  water  or  steam  which  appear  in  any  line  either  at  a 
valve,  flange,  or  other  fitting  should  be  stopped  immediately;  other- 
wise a serious  waste  of  fuel  may  result  in  making  up  the  heat  so  lost. 
An  even  more  serious  condition  may  result  if  a leak  is  so  located 
that  it  discharges  water  or  steam  over  any  part  of  the  boiler  or  over 
another  pipe  since  corrosion  is  very  rapid  in  such  a case.  In  fact, 
such  leaks  have  started  corrosion  which  later  resulted  in  boiler 
explosions. 

27.  Size  of  Steam  and  Exhaust  Mains—  The  size  and  length 
of  steam  and  exhaust  mains  may  adversely  affect  the  fuel  consump- 
tion of  a plant  if  these  lines  are  either,  (1)  too  small,  or  (2)  too 
large  for  the  proper  handling  of  the  steam  they  have  to  carry.  Gen- 
erally, the  lines  are  too  small,  but  this  is  not  always  the  case. 

If  the  steam  main  between  boiler  and  engine  is  too  small  or  too 
long,  it  will  be  necessary  to  carry  a much  higher  pressure  at  the 
boiler  than  would  otherwise  be  necessary  in  order  to  get  the  required 
pressure  at  the  engine.  The  excessive  friction  in  small  steam  lines 
causes  this  loss  in  pressure,  and  if  the  main  is  also  very  long  the 
loss  will  be  still  more  pronounced.  Steam  gages  at  the  boiler  and  at 
the  engine  throttle  should  not  show  a difference,  or  a drop  in  pres- 
sure of  more  than  five  pounds  when  the  engine  is  running  at  full 
capacity.  Should  it  be  necessary  to  carry  a much  higher  pressure 
at  the  boiler  than  at  the  engine  in  order  to  get  a satisfactory  opera- 
ting pressure,  some  unnecessary  coal  must  be  burned  since  all  the 
heat  losses  will  be  slightly  increased  and  leaks  will  be  somewhat 
more  likely  to  develop. 

On  the  other  hand,  if  this  main  is  too  large  (which  is  not  so 
serious)  the  pressure  at  the  engine  throttle  will  be  almost  the  same 
as  that  at  the  boiler  when  running  at  full  capacity.  The  heat  losses 
from  oversize  pipes  and  fittings  are  greater  and  the  first  cost  of 
installation  is  higher  than  for  mains  of  the  proper  size. 

In  the  case  of  the  exhaust  main,  the  size  is  most  important  since 
the  steam  has  now  expanded  and  occupies  a much  greater  volume 
than  when  it  left  the  boiler.  This  exhaust  steam  must  be  discharged 
from  the  engine  at  the  lowest  possible  back  pressure  if  the  engine  is 
to  get  the  most  work  out  of  each  pound  of  steam  supplied  to  it  and 


THE.  LIB8ABK 
OF  THE 


raESsmf  c::  n 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


73 


hence  develop  the  greatest  power.  With  exhaust  piping  which  is  too 
small,  a steam  gage  on  the  line  will  show  a back  pressure  of  more  than 
two  pounds  which  means  that  more  steam  is  being  taken  into  the 
engine  to  do  the  work  than  is  necessary.  This  in  turn  means  coal 
wasted.  Exhaust  mains  are  almost  never  too  large,  but  in  such  cases 
the  excess  heat  loss  due  to  radiation  from  large  exhaust  mains  is  not 
so  serious  as  in  the  case  of  high  pressure  steam  mains  since  the  tem- 
perature of  exhaust  steam  is  very  much  less  than  that  of  live  steam. 

28.  Heat  Insulating  Materials  Required  on  Piping , Boilers,  and 
Breechings. — The  desirability  of  covering  or  insulating  all  high  tem- 
perature surfaces  around  a boiler  and  power  plant,  when  fuel  is  as 
expensive  and  as  difficult  to  obtain  as  at  present,  is  self  evident.  It 
can  be  shown  that  by  covering  all  steam  and  hot-water  pipes,  fit- 
tings, flanges,  and  valves  enough  heat  can  be  saved  as  compared  with 
the  loss  from  bare  pipe  to  pay  for  the  labor  and  covering  material  in 
a very  few  months.  This,  of  course,  applies  to  the  ordinary  com- 
mercial coverings  ranging  from  one  to  two  inches  in  thickness.  Table 
5 shows  the  saving  per  year  for  100  feet  of  covered  pipe  in  pounds 
of  coal  and  in  dollars  with  coal  at  $5.00  per  ton  (2,000  pounds). 

The  best  commercial  coverings  one  inch  in  thickness  will  save 
or  prevent  the  escape  of  from  75  per  cent  to  85  per  cent  of  the  heat 
lost  from  bare  pipes.  The  thickness  of  the  covering  should  be  varied 
with  the  temperature  of  the  steam  or  water  in  the  pipe  line,  but  in 
general  it  will  pay  to  use  not  less  than  one  inch  on  all  lines  which  are 
at  200  degrees  F.  and  up  to  300  degrees  F.  Above  300  degrees  F. 
and  up  to  400  degrees  F.  it  is  advisable  to  use  iy2  inch  covering  and 
above  400  degrees  F.,  not  less  than  two  inches. 

The  actual  heat  saving  value  of  commercial  pipe  coverings  now 
on  the  market  has  been  the  subject  of  many  investigations.  The 
latest  work  in  this  field  has  been  done  by  L.  B.  McMillan  * at  the 
University  of  Wisconsin  and  the  charts  (Figs.  16  and  17)  have  been 
made  from  the  results  of  his  tests  on  bare  and  covered  five-inch  steel 
pipe.  These  charts  show  how  the  heat  transmitted  by  bare  pipe  com- 
pares with  the  heat  transmitted  by  the  same  pipe  when  insulated. 
The  values  of  only  seven  of  the  twenty  or  more  coverings  tested  are 
shown.  Their  efficiency  as  insulators  is  easily  seen  by  reading  the 

* “The  Heat  Insulating  Properties  of  Commercial  Steam  Pipe  Coverings,”  Journal, 
A.  S.  M.  E.,  Dec.,  1915. 


74  ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


75 


0.95 


0.90 


0.65 


Carves  taken  from  " The  Meat  l 'nsuiatmg  Properties  of  Com- 
mercial Of  earn  Pipe  Coverings  " LB.McMillan  A5M.E.  Dec.  1915 


'0.65 

£ ^ 

-Si  0..55 

t>s 

i^0.45 
& 

<p0.40 

0.30 


50  100  750  300  EDO  300  350  400  450  500 

Temperature  difference  /n  cfegreeo  Fahrenheit 
between  pipe  and  room  temperatures. 

Fig.  16.  Chart  Showing  Amount  of  Heat  Transmitted  by  Steam  Pipes  In- 
sulated with  Commercial  Coverings  (See  Fig.  17  for  Bare  Pipe.) 


76 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


5 K' 
^ k ■« 
^ ^.4 


O 50  100  150  200  250  300  350  400  450 

Temperature  difference  in  degrees  rahrenhe/t 
between  pipe  and  room  temperatures. 

Fig.  17.  Chart  Showing  Heat  Lost  by  Bare  Steam  Pipe  and  Saving  which 
May  be  Secured  by  Using  a Good  Covering 


scale  at  the  left  of  the  chart,  which  shows  the  heat  lost  or  transmitted 
per  hour  per  square  foot  of  pipe  surface  per  degree  difference  of 
temperature  between  the  steam  in  the  pipe  and  the  air  outside.  The 
heat  loss  is  expressed  in  B.  t.  u.* 


* For  a definition  of  B.  t.  u.  see  foot-note,  p.  17. 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


77 


The  importance  of  covering  steam  lines  operating  at  high  pres- 
sures and  temperatures  is  emphasized  by  Fig.  17.  It  will  be  seen  by 
reference  to  the  upper  curve  in  this  diagram  that  the  heat  loss  per 
square  foot  from  an  uncovered  five-inch  steam  line  increases  very 
rapidly  as  the  temperature  of  the  steam  in  the  line  increases.  By 
covering  the  line  with  a good  insulator,  not  only  is  a large  saving 
effected  by  reducing  the  heat  loss  (see  shaded  area),  but  the  increase 
in  the  heat  loss  per  square  foot  from  such  a covered  line  at  high 
temperatures  is  very  much  less  than  for  a bare  pipe. 

In  other  words,  it  is  most  important  to  cover  all  high  tempera- 
ture surfaces  which  are  in  contact  with  the  air. 

The  chart  (Fig.  17)  shows  that  with  steam  which  is  300  degrees 
F.  above  the  temperature  of  the  outside  air  a five-inch  diameter 
standard  bare  steel  pipe  transmits  about  3.3  B.  t.  u.  per  square  foot 
per  hour,  while  the  same  pipe  covered  with  “Nonpariel  High  Pres- 
sure Covering”  transmits  (Fig.  16)  only  0.425  B.  t.  u.  per  hour  or 
thirteen  per  cent  of  the  heat  wasted  by  the  bare  pipe.  In  other 
words  about  seven-eighths  of  the  loss  has  been  stopped  by  the  cover- 
ing. 


29.  Requirements  for  a Good  Covering. — A satisfactory  pipe 
covering  must  be,  (1)  unaffected  by  heat  or  fire,  (2)  easily  molded 
and  light  in  weight,  (3)  impervious  to  or  unaffected  by  water  and 
steam,  (4)  non-corrosive  in  its  effect  upon  metals  (steel,  iron  and 
brass),  (5)  structurally  fairly  strong  or  self  sustaining,  and  (6) 
sanitary  and  not  attractive  to  vermin  of  any  kind.  The  market 
affords  a great  variety  of  materials  at  various  prices  which  are  used 
for  this  purpose.  But  the  purchaser  must  remember  that  he  is  buy- 
ing heat  insulation,  not  merely  covering,  and  he  must  assure  himself 
that  the  material  is  a practical  and  effective  insulator. 

In  this  connection,  it  should  be  noted  that  the  soot  which  col- 
lects on  the  boiler  tubes  where  no  insulation  is  desired  is  several 
times  as  good  an  insulator  as  asbestos,  and  that  the  fine  ash  which 
also  collects  on  the  tubes  is  almost  as  good  an  insulator  as  soot.  In 
other  words,  if  it  is  advisable  and  economical  to  cover  steam  pipes 
with  insulation,  it  is  decidedly  more  economical  and  necessary  to  keep 
boiler  tubes  absolutely  clean  and  free  from  the  insulating  effects  of 
soot  and  ashes  at  all  times.  A similar  argument  applies  to  the  scale 
which  collects  on  the  water  side  of  the  tubes  or  shell  as  a result  of 


78 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


infrequent  cleaning  or  failure  to  employ  suitable  treatment  for  the 
feed  water. 

30.  Bad  Effects  of  Water  of  Condensation  in  Steam  Lines. — 
Not  only  does  an  uncovered  steam  line  waste  heat  by  transmission 
to  the  outside  air,  but  it  greatly  increases  the  condensation , require 
ing  the  boilers  to  furnish  more  steam  than  would  be  necessary  in  a 
covered  line.  It  also  adds  to  the  amount  of  water  to  be  handled  by 
the  traps,  and  results  in  excessive  wear  on  the  valve  seats  and 
through  the  steam  ports  of  the  engines.  If  a trap  fails  to  operate 
properly,  the  accumulated  water  may  travel  along  with  the  steam  at 
high  velocity  and  develop  a “water  hammer”  which  will  loosen  or 
break  some  fitting. 

31.  Uncovered  Pipes  Waste  Steam  as  Well  as  Coal. — The  owner 
of  a power  plant  should  realize  that  an  uncovered  steam  main  wastes 
heat  and  that  it  should  therefore  be  covered.  The  loss  of  heat  means 
a loss  of  steam  by  condensation  and  the  generation  of  steam  by  the 
boiler  plant  which  cannot  be  used. 

That  this  loss  is  serious  and  that  it  requires  the  boilers,  the  feed 
pumps,  and  the  traps  to  handle  much  more  water  than  would  be 
necessary  if  the  steam  mains  were  properly  covered  is  shown  by 
Fig.  18.  The  simple  computations  necessary  to  prove  this  statement 
for  a typical  case  are  given  below.  The  plant  shown  in  Fig.  18  is 
operating  24  hours  per  day  for  365  days  per  year.  A five-inch  steam 
main,  which  is  uncovered,  carries  steam  at  150  pounds  gage  pres- 
sure to  an  engine  100  feet  away.  The  air  around  the  main  averages 
70  degrees  F.  and  the  feed  water  enters  the  boiler  at  200  degrees  F. 

(1)  Actual  tests  show  that  each  square  foot  of  pipe  loses 
3.25  B.  t.  u.  per  hour  for  each  degree  of  difference  in  tem- 
perature between  steam  inside  and  air  outside  (Fig.  17). 

(2)  The  outside  surface  of  100  feet  of  five-inch  pipe  amounts  to 
145.6  square  feet. 

(3)  The  total  heat  loss  from  the  pipe  per  hour  is: 

3.25  X 145.6  X (366-70)  = 140,000  B.  t.  u. 

(The  temperature  of  saturated  steam  at  150-pound  gage  is 
366  degrees  F.) 

(4)  This  heat  is  obtained  by  condensing  not  by  cooling  some 
of  the  steam  in  the  pipe.  One  pound  of  steam  gives  up 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


79 


Note:  Each  tank  car  con  fa  ins  10,000  ga/s.  of  wafer 


80 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


858  B.  t.  u.  when  it  condenses  at  150  pounds  gage  pressure,  or 
the  uncovered  pipe  condenses  ^^’^^=163  pounds  per  hour.  - 

o5o 

(5)  In  one  year,  163  X 24  X 365  = 1,428,000  pounds  of  steam 
wasted;  that  is,  this  much  steam  never  reaches  the  engine. 
At  8 1-3  pounds  per  gallon,  171,200  gallons  of  water  have 
been  needlessly  handled. 

(6)  Expressed  in  another  way,  this  plant  has  evaporated  and 
sent  over  17  tank  ears  (of  10,000  gallons  capacity  per  car) 
of  water  into  this  line  which  did  not  perform  useful  work. 
This  represents  an  absolute  waste  of  coal,  of  steam,  and  of 
boiler  capacity.  At  least  75  per  cent  of  this  waste  could 
have  been  prevented  by  covering  the  line. 

(7)  To  evaporate  each  pound  of  this  water  from  feed  water  at 
200  degrees  F.  took  168  -|-  858  = 1,026  B.  t.  u.  or  a total  of 
1,026  X 103  = 167,300  B.  t.  u.  per  hour. 

(8)  At  60  per  cent  efficiency  each  pound  of  coal  (heat  value 
taken  as  12,000  B.  t.  u.  per  pound)  gives  to  the  boiler  7,200 
B.  t.  u.  or  the  plant  is  wasting  23.2  pounds  of  coal  per 
hour  to  supply  the  condensation  loss. 

(9)  The  coal  required  per  year  is: 

23.2  X 24  X 365  = 203,000  pounds  or  101.5  tons. 

(10)  This  means  that  this  plant  has  to  burn  about  2 y2  cars 
of  coal  (holding  40  tons  each),  in  order  to  provide  for  this 
annual  heat  loss.  A good  covering  would  stop  75  per  cent 
of  this  waste  and  save  two  whole  cars  or  80  tons  of  coal  a 
year.  Bare  steam  pipe  is  a very  expensive  luxury  in  any 
power  plant. 

The  cost  of  labor  and  material  for  covering  100  feet  of  the  five- 
inch  main  referred  to,  including  two  valves  and  six  fittings,  is  esti- 
mated at  about  $160.  This  is  based  on  present  day  conditions  with 
the  plant  located  within  150  miles  of  Chicago,  using  the  best  85  per 
cent  magnesia  sectional  covering,  of  IV2  inches  in  thickness.  The  use 
of  asbestos  sponge  felted  covering  would  not  add  more  than  four  or 
five  per  cent  to  this  estimate,  and  if  this  work  could  be  executed  as 
part  of  a large  covering  job  the  cost  could  be  reduced  about  twenty- 
five  or  thirty  per  cent. 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


81 


VIII.  Record  of  Operation 

32.  Purpose  of  the  Record. — The  maintenance  of  such  records 
of  operation  as  may  be  necessary  to  enable  the  superintendent  or 
owner  of  a plant  to  determine  with  reasonable  reliability  the  cost  of 
operation,  the  relative  efficiency  of  the  plant,  and  the  improvement 
from  time  to  time  is  essential.  For  practical  purposes,  the  index 
to  the  performance  of  any  steam  generating  plant  lies  in  the  relation 
between  the  number  of  pounds  of  water  evaporated,  and  the  number 
of  pounds  of  coal  fired  less  the  weight  of  the  ash.  The  record  must 
therefore  give  the  information  on  the  basis  of  which  this  relation 
may  be  determined  at  any  time,  and  it  should  also  contain  such  other 
data  as  may  be  required  for  detecting  and  remedying  any  defects  in 
operation  which  indicate  loss. 

33.  Character  of  the  Record. — It  must  be  recognized  that  no 
satisfactory  record  of  operation  is  possible  unless  the  plant  is  equipped 
with  certain  checking  and  recording  devices  which  have  been  recom- 
mended in  the  preceding  pages  of  this  discussion.  These  may  be  re- 
counted as  follows : 

(1)  Means  of  weighing  the  coal  fired  for  each  boiler. 

(2)  Means  of  weighing  the  ash  removed  from  the  pit. 

(3)  Some  device  for  weighing  or  measuring  the  water  fed  to 
the  boiler  or  the  steam  delivered  by  the  boiler. 

(4)  A thermometer  for  indicating  the  temperature  of  the  feed 
■water. 

(5)  A draft  gage  connected  into  the  space  above  the  fuel  bed 
and  into  the  ashpit. 

(6)  A differential  draft  gage  connected  into  the  space  above 
the  fuel  bed  and  into  the  flue  gas  passage  near  the  point 
of  discharge  from  the  boiler. 

(7)  A C02  analyzer. 

(8)  A pressure  gage  at  the  boiler  (pressure  gages  should  also 
be  supplied  at  the  ends  of  all  live  steam  lines). 

(9)  A pyrometer  for  indicating  the  temperature  of  the  flue 
gases  leaving  the  setting. 

Some  of  these  devices  are  already  part  of  the  equipment  of  most 


82 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


plants  and  the  others  may  be  secured  at  so  slight  a cost  in  proportion 
to  the  saving  to  be  effected  as  easily  to  warrant  their  installation. 

The  weighing  of  the  coal  does  not  present  any  difficulties.  The 
weighing  of  the  ashes,  however,  is  not  so  easy  owing  to  the  fact  that 
in  most  plants  the  ash  is  wetted  down  to  facilitate  handling  and  to 
the  possibility  of  a certain  amount  of  unconsumed  coal  being  present 
in  the  ash. 

The  function  to  be  performed  by  each  item  of  equipment 
included  in  the  foregoing  list  has  already  been  explained.  The  first 
four  items  are  necessary  for  arriving  at  the  relationship : 

Number  of  pounds  of  water  evaporated 
Number  of  pounds  of  ash  free  coal  fired 

The  last  five  items  of  equipment  listed  are  needed  to  indicate 
the  source  of  any  defects  in  operation  or  troubles  which  may  be 
leading  to  losses. 

The  daily  record  of  operation  should  include  the  items  shown  in 
the  form  given  on  page  83. 

Items  1,  2,  and  3 of  this  record  should  cover  the  entire  shift 
of  the  firemen  for  each  boiler.  Items  4 to  9,  inclusive,  should  con- 
- tain  readings  taken  for  each  boiler  at  regular  intervals  (the  sug- 
gested form  provides  for  hourly  readings)  throughout  the  shift  as 
frequently  as  may  be  practicable.  The  choice  of  the  individual  to 
be  charged  with  the  responsibility  of  maintaining  this  record  is  a 
matter  which  will  depend  largely  upon  the  character  and  size  of  the 
existing  organization  of  each  plant.  In  some  cases  it  may  be  found 
satisfactory  to  entrust  the  matter  to  the  fireman;  in  others  it  may 
be  desirable  to  assign  it  to  some  other  employe.  It  should  be  recog- 
nized in  any  case  that  unless  the  record  is  maintained  with  reason- 
able care  and  accuracy  its  value  is  not  great.  If  carefully  kept  the 
record  will  prove  a means  of  stimulating  the  interest  and  coopera- 
tion of  employes  concerned  with  the  operation  of  the  plant  as  well 
as  the  basis  for  effecting  economies  the  extent  of  which  will  in  most 
cases  be  material. 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


83 


NAME  OF  FIRM 

DAILY  'RECORD  OF  POWER  PLANT  OPERATION 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


84 


34.  Profit  Sharing  or  Bonus  Systems. — In  some  plants  the 
practice  is  followed  of  permitting  firemen  and  other  employes  to 
share  in  the  savings  which  result  from  their  efforts.  Without  under- 
taking either  to  commend  or  to  condemn  the  profit  sharing  system  as 
applied  to  power  plant  operation,  the  suggestion  is  offered  that  in 
any  event  no  such  system  should  be  inaugurated  until  the  plant  is 
put  in  proper  condition,  i.  e.,  until  the  setting  has  been  made  tight 
and  is  well  covered,  until  live  steam  pipes  are  covered,  and  until 
such  other  changes  have  been  made  and  devices  installed  as  have  been 
herein  discussed.  Having  made  these  mechanical  changes  and  im- 
provements, the  importance  of  which  will  be  reflected  in  the  results 
of  operation,  the  earnest  cooperation  of  employes  concerned  with 
the  plant  is  essential  in  securing  the  maximum  benefits,  and  the 
application  of  a profit  sharing  plan  may  in  some  cases  prove  the 
means  of  enlisting  this  cooperation. 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


85 


IX.  Summary  of  Conclusions 

35.  Conclusions. — To  enable  the  plant  owner  to  determine 
whether  or  not  his  installation  conforms  with  the  requirements  of 
practice  promoting  fuel  economy  and  to  check  up  his  methods  of 
operation,  the  essential  features  discussed  in  the  preceding  pages 
are  summarized  as  follows : 

Coal 

(1)  Practically  the  only  fuel  available  for  power  plant  use 
in  Illinois  under  present  conditions  is  bituminous  coal  from 
the  central  fields  of  Illinois,  Indiana,  and  western  Ken- 
tucky. 

(2)  The  care  with  which  coal  is  “prepared,”  and  separated 
into  different  sizes  is  an  important  factor  affecting  its  value 
in  the  power  plant. 

(3)  The  B.  t.  u.  value  and  the  percentage  of  ash  furnish  a 
general  guide  to  the  relative  values  of  Illinois  coals.  Gen- 
erally the  coals  having  the  lowest  ash  content  have  the 
highest  B.  t.  u.  value. 

(4)  The  storage  of  bituminous  coal  is  both  practicable  and 
desirable.  Certain  precautions,  however,  must  be  observed. 
These  are  set  forth  in  detail  on  page  18.* 

Principles  to  be  Observed  in  Firing 

(5)  The  three  fundamental  conditions  necessary  for  complete 
and  smokeless  combustion  of  bituminous  coal  are: 

(a)  A sufficient  amount  of  air  must  be  supplied. 

(b)  The  air  and  fuel  must  be  intimately  mixed. 

(c)  The  mixture  must  be  brought  to  the  ignition  tem- 
perature and  maintained  at  this  temperature  until 
combustion  is  complete. 

(6)  Since  bituminous  coal  from  the  central  field  is  practically 
the  only  fuel  available  at  present  for  power  plant  use  in 
Illinois  the  boiler  setting  and  the  plant  in  general  should 
be  adapted  to  the  economical  use  of  this  fuel. 

* See  also  Univ.  of  111.  Eng.  Exp.  Sta.  Circular  6,  entitled,  “The  Storage  of  Bituminous 
Coal,”  by  H.  H.  Stoek. 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


(7)  Every  boiler  should  be  equipped  with  two  draft  gages, 
one  connected  directly  in  the  space  over  the  fire,  and  one 
connected  both  into  the  space  over  the  fire  and  into  the  gas 
passage  below  the  damper.  For  every  given  load,  the  draft 
necessary  to  carry  it  and  the  proper  thickness  of  fuel  bed 
with  the  grade  of  coal  used  should  be  determined. 

(8)  In  many  plants  of  large  and  medium  size  automatic  draft 
control  has  proved  economical,  and  it  is  also  of  advantage 
in  maintaining  constant  steam  pressure. 

(9)  Every  plant  should  have  some  simple  type  of  C02  analyzer 
for  obtaining  a knowledge  of  conditions  existing  within 
the  furnace.  (See  page  30.) 

(10)  Air  leakage  through  the  boiler  setting  should  be  pre- 
vented by  properly  calking  and  covering  the  setting. 

(11)  Losses  due  to  the  presence  of  unconsumed  coal  in  the 
ash  should  be  avoided  by  seeing  that  the  fire  is  properly 
worked  and  that  the  grate  openings  are  not  too  large  for  the 
size  of  fuel  fired. 

(12)  Sooty  deposits  on  the  heating  surfaces  should  be  removed 
frequently.  Should  the  temperature  of  the  gases  leaving 
the  boiler  exceed  550  degrees  F.,  it  probably  indicates  that 
the  tubes  need  blowing. 

(13)  Scale  on  the  water  surfaces  of  the  boiler  should  not  be 
allowed  to  accumulate. 

(14)  The  spreading  method  of  firing  in  which  small  quantities 
of  coal  are  fired  at  frequent  intervals  is  regarded  as  a sat- 
isfactory method  for  hand  fired  plants.  (See  page  41.) 

Features  of  Boiler  Installation 

(15)  The  foundation  for  a boiler  setting  should  rest  on  a firm 
footing  in  order  to  insure  a setting  which  will  remain  tight 
and  free  from  any  tendency  to  crack. 

(16)  For  the  complete  combustion  of  bituminous  coal  boiler 
settings  must  provide  for  the  introduction  of  sufficient  air 
into  the  furnace,  for  the  proper  mixing  of  this  air  with  the 
gases  given  off  by  the  burning  coal,  and  for  the  mainte- 
nance of  a high  temperature  until  the  process  of  combustion 
is  complete.  This  is  to  be  accomplished  by  means  of  arches, 
baffles,  and  other  devices  as  hereinbefore  described.  (See 
page  44.) 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


87 


(17)  The  brick  work  in  setting  should  be  properly  pointed 
up  and  covered  with  an  insulating  material  to  prevent  air 
leakage.  The  exposed  parts  of  the  shell  of  horizontal 
return  tubular  boilers  and  of  the  steam  drums  of  water 
tube  boilers  should  be  covered  with  a high  grade  of  asbestos 
insulating  material  at  least  two  inches  thick,  or  with  an 
85  per  cent  magnesia  covering  two  or  three  inches  thick, 
and  the  outside  finished  off  with  a thin  coat  of  hard  cement 
or  covered  with  canvas  and  painted.  Air  spaces  in  the 
walls  of  the  setting  should  be  filled  with  sand  or  ashes. 

Stacks  and  Breechings 

(18)  In  order  to  control  the  amount  of  air  and  flue  gas  passing 
to  the  stack  a damper  installed  at  the  point  where  the  flue 
gas  leaves  the  boiler  should  be  regulated  so  as  to  permit  the 
stack  to  supply  the  right  amount  of  air  to  burn  completely 
the  fuel  fired.  The  air  supply  should  be  controlled  by  this 
damper  and  not  by  opening  and  closing  the  ashpit  doors, 
which  should  stand  open  practically  all  the  time.  Each 
boiler  should  have  its  individual  damper. 

(19)  The  individual  boiler  dampers  should  fit  accurately  and 
close  tight,  otherwise  it  will  be  impossible  to  prevent  cold 
air  from  entering  the  main  breeching  through  the  damper 
of  a “dead”  boiler. 

(20)  The  breeching  and  stack  should  be  made  air  tight  and 
should  be  insulated  to  prevent  heat  loss  from  the  flue  gases 
so  that  all  the  heat  in  the  gases  may  be  available  for  creat- 
ing draft. 

Feed  Water  and  Fuel 

(21)  If  the  feed  water  used  causes  scale,  corrosion,  or  priming 
it  should  be  analyzed  by  a reliable  chemist  and  treated  in 
such  manner  as  he  may  prescribe. 

(22)  It  is  necessary  and  economical  to  heat  the  feed  water. 
One  per  cent  of  fuel  is  saved  for  every  eleven  degrees  rise 
in  the  feed  water  temperature. 

(23)  For  the  majority  of  small  boiler  plants  the  feed  water 
should  be  introduced  into  the  boiler  at  a constant  rate 
rather  than  intermittently.  The  feed  water  system  should 
include  some  form  of  metering  device  for  measuring  the 
water  fed  to  the  boiler  or  the  steam  delivered  by  it. 


88 


ILLINOIS  ENGINEERING  EXPERIMENT  STATION 


(24)  Means  should  be  provided  for  weighing  the  coal  fired  to 
each  boiler  and  the  ash  removed. 

Steam  Piping  Requirements 

(25)  The  piping  system  should  be  as  simple  as  possible  and 
well  insulated.  Only  short  direct  runs  of  live  steam  pipes 
should  be  used  in  connecting  boilers,  engines,  and  other 
steam  using  apparatus. 

(26)  Each  high  pressure  header  and  steam  separator  should 
be  provided  with  drips  and  the  hot  water  returned  to  the 
feed  water  heater. 

(27)  Leakage  losses  at  valves  and  fittings  in  all  steam  and 
water  lines  should  be  stopped  at  once. 

(28)  If  a steam  main  is  either  too  small  or  too  long  it  will  be 
necessary  to  carry  a higher  pressure  at  the  boiler  to  get  the 
required  pressure  at  the  engine.  Steam  gages  at  the  boiler 
and  at  the  engine  throttle  should  show  a drop  in  pressure 
of  not  more  than  five  pounds  when  the  engine  is  running 
at  full  capacity.  If  a steam  main  is  too  large  the  pressure 
at  the  engine  throttle  will  be  almost  the  same  as  that  at 
the  boiler.  The  heat  losses  from  oversize  pipes  and  fittings 
are  somewhat  greater  and  the  cost  of  installation  is  higher 
than  for  mains  of  the  proper  size.  The  exhaust  piping 
should  be  of  such  size  that  a gage  near  the  engine  will 
show  a pressure  of  not  more  than  two  pounds. 

(29)  All  steam  and  hot  water  piping,  fittings,  flanges,  and 
valves  should  be  covered  with  an  insulating  material.  The 
saving  to  be  affected  by  such  covering  is  sufficient  to  repay 
the  cost  in  the  first  few  months.  (See  page  76.) 

Record  of  Operation 

(30)  A suitable  record  of  operation  should  be  maintained  upon 
the  basis  of  which  the  superintendent  or  owner  of  the  plant 
may  determine  with  reasonable  reliability  the  cost  of  opera- 
tion, the  relative  efficiency  of  the  plant,  and  the  improve- 
ment from  time  to  time.  From  the  record  of  operation  it 
should  be  possible  to  determine  whether  the  individual 
boilers  are  operating  at  their  rated  capacities.  In  cases  in 
which  boilers  are  operating  at  less  than  capacity  condi- 
tions should  be  so  changed  as  to  require  each  unit  to  carry 


FUEL  ECONOMY  IN  HAND  FIRED  POWER  PLANTS 


89 


its  full  load  or  an  overload.  In  cases  in  which  it  is  not  pos- 
sible to  balance  the  load  with  the  combined  capacity  of 
units,  it  is  economical  to  operate  as  many  boilers  as  pos- 
sible at  capacity  and  to  throw  the  excess  on  an  extra  unit. 

(31)  Special  emphasis  is  to  be  laid  upon  the  problem  of  the 
plant  owner  and  upon  the  part  he  must  play  in  the  program 
of  saving  fuel.  The  economical  utilization  of  fuel  in  power 
plants  is  vital,  not  so  much  because  it  means  a cash  saving  to 
the  owner,  but  rather  because  conditions  are  fast  approaching 
a point  at  which  the  owner  who  does  not  conserve  his  fuel 
may  find  himself  unable  to  maintain  continuous  operation. 


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PUBLICATIONS  OF  THE  ENGINEERING  EXPERIMENT  STATION 


Bulletin  No.  1.  Tests  of  Reinforced  Concrete  Beams,  by  Arthur  N.  Talbot,  1904.  None  available. 
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Circular  No.  2.  Drainage  of  Earth  Roads,  by  Ira  O.  Baker.  1906.  None  available. 

Circular  No.  3.  Fuel  Tests  with  Illinois  Coal  (Compiled  from  tests  made  by  the  Technological 
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Bulletin  No.  7.  Fuel  Tests  with  Illinois  Coals,  by  L.  P.  Breckenridge,  S.  W.  Parr,  and  Henry  B. 
Dirks.  1906.  None  available. 

Bulletin  No.  8.  Tests  of  Concrete:  I,  Shear;  II,  Bond,  by  Arthur  N.  Talbot.  1906.  None 
available. 

Bulletin  No.  9.  An  Extension  of  the  Dewey  Decimal  System  of  Classification  Applied  to  the 
Engineering  Industries,  by  L.  P.  Breckenridge  and  G.  A.  Goodenough.  1906.  Revised  Edition 
1912.  Fifty  cents. 

Bulletin  No.  10.  Tests  of  Concrete  and  Reinforced  Concrete  Columns,  Series  of  1906,  by  Arthur 
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Bulletin  No.  12.  Tests  of  Reinforced  Concrete  T-Beams,  Series  of  1906,  by  Arthur  N.  Talbot 

1907.  None  available. 

Bulletin  No.  13.  An  Extension  of  the  Dewey  Decimal  System  of  Classification  Applied  to  Archi- 
tecture and  Building,  by  N.  Clifford  Ricker.  1907.  None  available. 

Bulletin  No.  14-  Tests  of  Reinforced  Concrete  Beams,  Series  of  1906,  by  Arthur  N.  Talbot. 

1907.  None  available. 

Bulletin  No.  15.  How  to  Burn  Illinois  Coal  Without  Smoke,  by  L.  P.  Breckenridge.  1908 
None  available. 

Bulletin  No.  16.  A Study  of  Roof  Trusses,  by  N.  Clifford  Ricker.  1908.  None  available. 

Bulletin  No.  17.  The  Weathering  of  Coal,  by  S.  W.  Parr,  N.  D.  Hamilton,  and  W.  F.  Wheeler. 

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Bulletin  No.  18.  The  Strength  of  Chain  Links,  by  G.  A.  Goodenough  and  L.  E.  Moore.  1908. 
Forty  cents. 

Bulletin  No.  19.  Comparative  Tests  of  Carbon,  Metallized  Carbon  and  Tantalum  Filament 
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Bulletin  No.  20.  Tests  of  Concrete  and  Reinforced  Concrete  Columns,  Series  of  1907,  by  Arthur 
N.  Talbot.  1908.  None  available. 

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Bulletin  No.  23.  Voids,  Settlement  and  Weight  of  Crushed  Stone,  by  Ira  O.  Baker.  1908. 
Fifteen  cents. 

* Bulletin  No.  24 ■ The  Modification  of  Illinois  Coal  by  Low  Temperature  Distillation,  by  S.  W.  Parr 
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Bulletin  No.  25.  Lighting  Country  Homes  by  Private  Electric  Plants  by  T.  H.  Amrine.  1908. 
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Bulletin  No.  28.  A Test  of  Three  Large  Reinforced  Concrete  Beams,  by  Arthur  N.  Talbot. 
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Bulletin  No.  68.  Entropy-Temperature  and  Transmission  Diagrams  for  Air,  by  C.  R.  Richards. 

1913.  Twenty-five  cents. 

* Bulletin  No.  64-  Tests  of  Reinforced  Concrete  Buildings  Under  Load,  by  Arthur  N.  Talbot  and 
Willis  A.  Slater.  1913.  Fifty  cents. 

* Bulletin  No.  65.  The  Steam  Consumption  of  Locomotive  Engines  from  the  Indicator  Diagrams, 
by  J.  Paul  Clayton.  1913.  Forty  cents. 

Bulletin  No.  66.  The  Properties  of  Saturated  and  Superheated  Ammonia  Vapor,  by  G.  A.  Good- 
enough  and  William  Earl  Mosher.  1913.  Fifty  cents. 

Bulletin  No.  67.  Reinforced  Concrete  Wall  Footings  and  Column  Footings,  by  Arthur  N.  Talbot. 

1913.  Fifty  cents. 

*Bulletin  No.  68.  The  Strength  of  I-Beams  in  Flexure,  by  Herbert  F.  Moore.  1913.  Twenty 
cents. 

Bulletin  No.  69.  Coal  Washing  in  Illinois,  by  F.  C.  Lincoln.  1913.  Fifty  cents. 

Bulletin  No.  70.  The  Mortar-Making  Qualities  of  Illinois  Sands,  by  C.  C.  Wiley.  1913.  Twenty 
cents. 

Bulletin  No.  71.  Tests  of  Bond  between  Concrete  and  Steel,  by  Duff  A.  Abrams.  1913.  One 
dollar. 

*Bulletin  No.  72.  Magnetic  and  Other  Properties  of  Electrolytic  Iron  Melted  in  Vacuo,  by  Trygve 
D.  Yensen.  1914.  Forty  cents. 

Bulletin  No.  73.  Acoustics  of  Auditoriums,  by  F.  R.  Watson.  1914.  Twenty  cents. 

*Bulletin  No.  74.  The  Tractive  Resistance  of  a 28-Ton  Electric  Car,  by  Harold  H.  Dunn.  1914. 
Twenty-five  cents. 

Bulletin  No.  75.  Thermal  Properties  of  Steam,  by  G.  A.  Goodenough.  1914.  Thirty-five  cents. 

Bulletin  No.  76.  The  Analysis  of  Coal  with  Phenol  is  a Solvent,  by  S.  W.  Parr  and  H.  F.  Hadley. 

1914.  Twenty-five  cents. 

* Bulletin  No.  77.  The  Effect  of  Boron  upon  the  Magnetic  and  Other  Properties  of  Electrolytic 
Iron  Melted  in  Vacuo,  by  Trygve  D.  Yensen.  1915.  Ten  cents. 

*Bulletin  No.  78.  A Study  of  Boiler  Losses,  by  A.  P.  Kratz.  1915.  Thirty-five  cents. 

*Bulletin  No.  79.  The  Coking  of  Coal  at  Low  Temperatures,  with  Special  Reference  to  the  Prop- 
erties and  Composition  of  the  Products,  by  S.  W.  Parr  and  H.  L.  Olin.  1915.  Twenty-five  cents. 

*Bulletin  No.  80.  Wind  Stresses  in  the  Steel  Frames  of  Office  Buildings,  by  W.  M.  Wilson  and 
G.  A.  Maney.  1915.  Fifty  cents. 

*Bulletin  No.  81.  Influence  of  Temperature  on  the  Strength  of  Concrete,  by  A.  B.  McDaniel. 

1915.  Fifteen  cents. 

Bulletin  No.  82.  Laboratory  Tests  of  a Consolidation  Locomotive,  by  E.  C.  Schmidt,  J.  M.  Snod- 
grass, and  R.  B.  Keller.  1915.  Sixty-five  cents. 

*Bulletin  No.  83.  Magnetic  and  Other  Properties  of  Iron-Silicon  Alloys.  Melted  in  Vacuo,  by 
Trygve  D.  Yensen.  1915.  Thirty-five  cents. 

Bulletin  No.  84.  Tests  of  Reinforced  Concrete  Flat  Slab  Structure,  by  Arthur  N.  Talbot  and 
W.  A.  Slater.  1916.  Sixty-five  cents. 

*Bulletin  No.  85.  The  Strength  and  Stiffness  of  Steel  Under  Biaxial  Loading,  by  A.  T.  Becker. 

1916.  Thirty-five  cents. 

*Bulletin  No.  86.  The  Strength  of  I-Beams  and  Girders,  by  Herbert  F.  Moore  and  W.  M.  Wilson. 
1916.  Thirty  cents. 

*Bulletin  No.  87.  Correction  of  Echoes  in  the  Auditorium,  University  of  Illinois,  by  F.  R.  Watson 
and  J.  M.  White.  1916.  Fifteen  cents. 

Bulletin  No.  88.  Dry  Preparation  of  Bituminous  Coal  at  Illinois  Mines,  by  E.  A.  Holbrook.  1916. 
Seventy  cents. 


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94 


PUBLICATIONS  OF  THE  ENGINEERING  EXPERIMENT  STATION 


* Bulletin  No.  89.  Specific  Gravity  Studies  of  Illinois  Coal,  by  Merle  L.  Nebel.  1916.  Thirty 

cents. 

*Bulletin  No.  90.  Some  Graphical  Solutions  of  Electric  Railway  Problems,  by  A.  M.  Buck. 

1916.  Twenty  cents. 

Bulletin  No.  91.  Subsidence  Resulting  from  Mining,  by  L.  E.  Young  and  H.  H.  Stoek.  1916. 
One  dollar. 

* Bulletin  No.  92.  The  Tractive  Resistance  on  Curves  of  a 28-Ton  Electric  Car,  by  E.  C.  Schmidt 
and  H.  H.  Dunn.  1916.  Twenty-five  cents. 

* Bulletin  No.  93.  A Preliminary  Study  of  the  Alloys  of  Chromium,  Copper,  and  Nickel,  by 

D.  F.  McFarland  and  O.  E.  Harder.  1916.  Thirty  cents. 

* Bulletin  No.  94.  The  Embrittling  Action  of  Sodium  Hydroxide  on  Soft  Steel,  by  S.  W.  Parr. 

1917.  Thirty  cents. 

* Bulletin  No.  95.  Magnetic  and  Other  Properties  of  Iron-Aluminum  Alloys  Melted  in  Vacuo,  by 
Trygve  D.  Yensen  and  W.  A.  Gatward.  1917.  Twenty-five  cents. 

* Bulletin  No.  96.  The  Effect  of  Mouthpieces  on  the  Flow  of  Water  Through  a Submerged  Short 
Pipe,  by  Fred  B.  Seely.  1917.  Twenty-five  cents. 

* Bulletin  No.  97.  Effects  of  Storage  Upon  the  Properties  of  Coal,  by  S.  W.  Parr.  1917.  Twenty 
cents. 

* Bulletin  No.  98.  Tests  of  Oxyacetylene  Welded  Joints  in  Steel  Plates,  by  Herbert  F.  Moore. 
1917.  Ten  cents. 

Circular  No.  4-  The  Economical  Purchase  and  Use  of  Coal  for  Heating  Homes,  with  Special 
Reference  to  Conditions  in  Illinois.  1917.  Ten  cents. 

* Bulletin  No.  99.  The  Collapse  of  Short  Thin  Tubes,  by  A.  P.  Carman.  1917.  Twenty  cents. 

* Circular  No.  5.  The  Utilization  of  Pyrite  Occurring  in  Illinois  Bituminous  Coal,  by  E.  A. 
Holbrook.  1917.  Twenty  cents. 

* Bulletin  No.  100.  Percentage  of  Extraction  of  Bituminous  Coal  with  Special  Reference  to  Illinois 
Conditions,  by  C.  M.  Young.  1917. 

* Bulletin  No.  101.  Comparative  Tests  of  Six  Sizes  of  Illinois  Coal  on  a Mikado  Locomotive,  by 

E.  C.  Schmidt,  J.  M.  Snodgrass,  and  O.  S.  Beyer,  Jr.  1917.  Fifty  cents. 

* Bulletin  No.  102.  A Study 'of  the  Heat  Transmission  of  Building  Materials,  by  A.  C.  Willard 
and  L.  C.  Lichty.  1917.  Twenty-five  cents. 

* Bulletin  No.  103.  An  Investigation  of  Twist  Drills,  by  Bruce  W.  Benedict  and  W.  P.  Lukens. 
1917.  Sixty  cents. 

* Bulletin  No.  10 4-  Tests  to  Determine  tjie  Rigidity  of  Riveted  Joints  of  Steel  Structures,  by 
W.  M.  Wilson  and  H.  F.  Moore.  1917.  Twenty-five  cents. 

Circular  No.  6.  The  Storage  of  Bituminous  Coal,  by  H.  H.  Stoek.  1918.  Forty  Cents. 

Circular  No.  7.  Fuel  Economy  in  the  Operation  of  Hand  Fired  Power  Plants.  1918. 
Twenty  cents. 


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THE  UNIVERSITY  OF  ILLINOIS 
THE  STATE  UNIVERSITY 
Urbana 

Edmund  J.  James,  Ph.D.,  LL.D.,  President 


THE  UNIVERSITY  INCLUDES  THE  FOLLOWING  DEPARTMENTS: 
The  Graduate  School 

The  College  of  Liberal  Arts  and  Sciences  (Ancient  and  Modern  Languages  and 
Literatures;  History,  Economics,  Political  Science,  Sociology;  Philosophy, 
Psychology,  Education;  Mathematics;  Astronomy;  Geology;  Physics;  Chemis- 
try; Botany,  Zoology,  Entomology;  Physiology;  Art  and  Design) 

The  College  of  Commerce  and  Business  Administration  (General  Business,  Bank- 
ing, Insurance,  Accountancy,  Railway  Administration,  Foreign  Commerce; 
Courses  for  Commercial  Teachers  and  Commercial  and  Civic  Secretaries) 

The  College  of  Engineering  (Architecture;  Architectural,  Ceramic,  Civil,  Electrical, 
Mechanical,  Mining,  Municipal  and  Sanitary,  and  Railway  Engineering) 

The  College  of  Agriculture  (Agronomy;  Animal  Husbandry;  Dairy  Husbandry; 
Horticulture  and  Landscape  Gardening;  Agricultural  Extension;  Teachers’ 
Course;  Household  Science) 

The  College  of  Law  (three  years’  course) 

The  School  of  Education 

The  Course  in  Journalism 

The  Courses  in  Chemistry  and  Chemical  Engineering 
The  School  of  Railway  Engineering  and  Administration 
The  School  of  Music  (four  years’  course) 

The  School  of  Library  Science  (two  years’  course) 

The  College  of  Medicine  (in  Chicago) 

The  College  of  Dentistry  (in  Chicago) 

The  School  of  Pharmacy  (in  Chicago;  Ph.  G.  and  Ph.  C.  courses) 

The  Summer  Session  (eight  weeks) 

Experiment  Stations  and  Scientific  Bureaus:  U.  S.  Agricultural  Experiment 
Station;  Engineering  Experiment  Station;  State  Laboratory  of  Natural  His- 
tory; State  Entomologist’s  Office;  Biological  Experiment  Station  on  Illinois 
River;  State  Water  Survey;  State  Geological  Survey;  U.  S.  Bureau  of  Mines 
Experiment  Station. 

The  library  collections  contain  (December  1,  1917)  411,737  volumes  and  104,524 
pamphlets. 


For  catalogs  and  information  address 


THE  REGISTRAR 
Urbana,  Illinois 


■ 


UNIVERSITY  OF  ILLINOIS-URBANA 


3 0112  067251923 


